Is he neutered? Sometimes dogs can have a leaking issue after they are altered. If it's not medical, and what has the vet prescribed for the worms? How have you already tried to get rid of them?
I would suggest trying to dig out the grass an area and level it off with some small rocks or other easily hosed down material that can be sprayed and cleaned. Help designate a spot for your pup (adorable by the way) What I did to train my dog was as soon as he woke we would go outside to the same spot, each time. Then every half hour or when he moved we would go to the spot and do the routine. I would ask him if he wanted to go outside and then bring him to the door and have him sit and get his leash on and go. Every half hour, seriously. If he stopes playing with a toy or chewing for a while and got up, I did the routine and took him outside. He sits at your feet or is laying down and gets up, take him outside. When he goes the bathroom only (going out often he may not have to go) praise him and give so much love you would think he just shit a gold brick if someone heard you! lol Associate outside with leash and a word (bathroom, poops, business whatever you want to call it so when you praise yay good bathroom or whatever) and same location to go and sit and he will learn soon what you're expecting. My boy was able to be pretty reliable after week or two. ABSOLUTELY no unsupervised time out free around the house. Set up a pen or a crate so he does not have the ability to go when you aren't watching and taking him out every half hour.