I hate to tell you this, but it took well over a year before she was fully house trained. We offered her a treat whenever she pooped or peed after we took her outside. It also took some time to realize she has GI issues and doesnt tolerate a lot of the dog foods on the market. A lot of the foods gave her diarrhea, which made house training more difficult. We learned we have to feed her only grain-free food, which has cut down on her BMs.
Once your dog gets into a routine with his/her schedule, try to learn the bathroom habits; does he/she poop or pee first thing in the morning, or later? We took our dog outside frequently to poop or pee. When we couldnt be home with her, she had to stay in her crate, or she was limited to one room. It really did take quite a while for her to become fully trained. I think it has to do with your dog bonding with you and wanting to please you as well.
Our dog is 4 now, shes never in a crate, and she has free reign of the house at all times. She hasnt had an accident in the house for at least the last 1 1/2 years. She is very happy and wants to please us, so I think she knows we dont want her doing her business in the house.
If your dog is 3 and not house-trained, it may take more time to train him/her. Puppies can learn more quickly, adult dogs take longer.