Male pitbull growls at owner
I have a three years old male American Staffordshire Terrier. He is very sweet and calm with people and other animals. I never had a problem with him before. About a month ago, I was sitting on the coach watching tv and petting him at the back of his neck, when he started growling. I didn't pay any attention because I thought that he had heard something from the street and I continued petting him. Then, he turned at me and made a move like he wanted to bite me, but he never actually put my hand in his mouth. He just showed me his teeth and moved his head towards me. As soon as he did that, I yield at him and he went to hide himself underneath the bed. I left him there for a while, and when I went to tell him to go outside, he started growling again. At the end, he went outside and for the next couple of days, he was acting like he knew he had done something bad. He was all sweet and obedient like before.
Last weekend we went to my countryhouse where he was running, swimming and playing with another dog all day. At the evening, he was tired enough and he sat besides me while I was plaing cards with some friends. Out of nowhere, as I was petting him unconsiously, he growled at me and showed me his teeth.
I wanted to add that the dog used to be very playful with other dogs, but unfortunately the other dogs were scared of him. He has never been aggressive to other animals. Lately, he started to try hump every dog he came to contact with. The other day a friend of mine brought home a female labrador puppy (2.5 months old) and he was constantly humping her. he did the same with an adult male dog. I have not neutered him and he has never mate, so maybe this is his way of showing to the other dogs "who is the boss".
I don't know what this behavior means and if the dog is trying to tell me something. I don't have a lot of experience with this breed, so any help would be very appreciated.I am really worried with his behavior towards me and I want to find a way to fix it. Do you think that the two 'problems' are related?