All dog owners please help!?

My dog is infested with fleas, but were having problems getting rid of them! We gave him lots of medicine for them, but none of it's working! We even went to the doctor and got him pills for it and it's still not working. Our dog is an inside dog so when he comes back in from his potty run he comes back in our house. Probably spreading the fleas everywhere but no matter what we do we can't get rid of them. We wanted to treat our yard but we don't have enough money right now. Can someone please recommend any suggestions you might have to this problem? Please before they spread even more.