Well puppies all train at their own pace, and 4-months-old is very young. The bladder is not grown until 6-months-old. Here are some potty training tips, use what helps, and leave the rest.
I use a crate* to potty train with, but only for potty training and then I break it down and store it. I put blankets and a small food and water dish in the crate. Dogs don't potty where they eat and sleep. When they are first little, I only expect them to hold their potty for 4 hours, and then 6 hours, then 8 hours and so on. So when they are first little, I set a timer or alarm clock to wake myself up at night to take them *out. I only allow my puppy in the bedroom* or the living room, only one room at a time. They have to graduate to more space. If I allow them to have full run of the house, it will overwhelm them. I take them out the same door each time. I tie a dinner bell to the door handle. Do not use a jingle bell as they could get their toe caught in it. So when they are little, I ring the bell for them, and then open the door to go *outside to potty. When they get bigger, I take their paw and whack the bell and open the door to go potty. Eventually getting to the place where the puppy will ring the bell and let me know when they need to go potty. Dogs want to please you, so it is your job to let them know what behaviors please you and what doesn't. So when my puppy goes potty, I give her a treat*, and clap, and make a fuss and praise her. So she learns that going potty outside makes me happy. If she has an accident make a disgust sound like “tsst” and take her out right away. I never yell* or spank* my puppies. Take them out when they first wake up, after they eat or drink, before nap, finish romping, when their activities change, or when they are sniffing around. Some puppies go pee right away, but may not go poop until 10 minutes later, so wait for the poop. I have a little play time here, because sometimes I think they are done, and they are not. Puppies train at their own pace. While I may have a puppy that hasn't had an accident in several weeks, I don't let my guard down. I don't expect my puppies to be "fully potty trained" until one-year-old. If they have a setback, shake it off, and start over. I only have my puppies in the crate when I am not watching them. When I am sleeping, cooking, ironing, doing chores, basically when I am not watching her. All other times, she is out of the crate practicing being a "big girl." This is the time I train her how to behave in the house. So we are practicing "no barking", 'no biting", "no jumping", and "don't eat the furniture." I also have to practice "playing inside" so she doesn't knock over things. You must keep the puppy in sight when they are little because they don’t know the difference between newspaper and carpet, and you don’t want them sneaking off and getting into trouble. Some puppies can sleep through the night around 3-months-old, but their bladder is grown around 6-months-old.
*I use a crate to train with. It is the method I prefer, compared to other methods I have tried. While personally, the crate traumatizes me, (it looks like a doggie jail), my puppies do better in the crate. They like it, I guess for the den like feeling, but I noticed that if they are in the crate, while I am doing chores, they are o.k., because the crate allows them to see me and be re-assured. The crate can also be a comfort when stored in the basement for dogs who live in areas where thunderstorms and tornados are an issue. It is a safe secure place for them. However, use the method that works best for you.....a laundry basket, a cardboard box, a woof-woof house, child gates......whatever works for you.
*Outside, pee pad, litter box, whichever method you are using. When the puppy is first little, keep the pee pad, litter box near the food and water dish, so the puppy can eat and drink, and then go potty. You can move it away as they get older. The pee pad has a scent that smells and initiates potty. Sometimes a pee pad makes a sound that scares some puppies, so you might want to use a litter box if that happens. The pee pad allows a puppy to walk around, but a litter box keeps the puppy in one place.
*Bedrooms, I use the bedroom and living room for training, because it works for me. Choose rooms that work for you, but watch for rooms that are damp, or drafty. While my puppies sleep in the bedroom during training, once they are trained, I let them sleep where they want to. They don't have to sleep in the bedroom forever.
*Treats. While I use treats for training, you don't have to. I like Charlee Bears for training (a little cracker for a little mouth,) I use them for training, but once they are trained, I cut back on them. Although I use them to give them pills too. I used different treats for different things. We use one bone at bedtime to let the dogs know it is time to go to bed. We use a big rawhide for when we go on long trips, so they have a bone to amuse them, and they will be expected to hold their potty. When they get the rawhide, they will not eat their food and water, until we get home from our trip. (dogs are funny) Do what works best for you.
*Some puppies will go potty in the same spot each time. Some puppies have to be told to go potty. A command like "go out" for pee, or "go finish" for poop, might work for you, keep saying “go finish” until the puppy poops. This is a good thing to train if you travel with your dogs. By using commands, the puppy won't get confused when you are visiting someone, on vacation with you, or when you get to a new home. The command will tell them what you want them to do in an unfamiliar place. You might also want to use a leash method, so the puppy doesn’t sneak off, or for strange places.
*Yelling. It is not a good idea to "yell" or "spank" your puppy and then take them outside when they have an accident. They may get confused and think that going outside is punishment. While you want to correct them, if you are extreme, they may not want to go outside again. Shake it off, and resume your schedule. You have to keep it real. Puppies train at their own pace, but a puppy can only hold their potty for a few hours. A guide would be 1 hour for each month of age, plus 1 hour, so a three-month-old puppy should only be expected to hold their potty for 4 hours at most.
*Sometimes it seems like you take your puppy out 5 million times a day. You can sit on a bench, or folding chair, or a 5 gallon bucket turned upside down to stay in the shade. I use an umbrella for shade too. You can always tape your favorite tv shows. In the winter I microwave a gel pack heating pad, (sold at walmart in the pharmacy, made by Kaz, (I think.) I put the heating pad under my jacket so I won't freeze to death. In the summer, I freeze bottles of water, so we can grab one real fast on our way out the door. I have a mini back pack by the door I can just grab with doggie treats, a flash light, a rubber band for my hair when the wind is bad, etc. Do what works for you.
*Time lines. Keep it real. Puppies train at their own pace, so while your last 2 dogs may have trained faster, this puppy might take longer. Training is all about routines, and repeating yourself. It is about rewarding good behaviors, and correcting bad ones. If you have a setback, shake it off, and keep going. Good luck.
Source: These tips, tricks, and ideas were contributed from many brilliant minds. Thanks for your help!