Hi there and Welcome to YT! Congrats on your new puppy!
First and foremost, it's always best to call your Vet whenever you think there is a problem with your puppy. And you should probably give him a call today.
However, it sort of sounds as if he is constipated. And one of the problems that makes it appear that way is the gathering of feces on his little bum. It was good that you cleaned that away and is something you want to look at every day to make sure it stays clean so that he has a clear passage.
As far as why he is constipated it could be a few things. Did you change his food, give him "people" food, or did he get into the trashbin? Either way, if it's simply constipation, pumpkin (100% pure with no spices) is a good food to use for both diarrhea and constipation.
Again, give you Vet a quick call and see whe he/she says.
Good luck!