I have a pit bull and he is about 3yrs old. I had him since he was 6wks old. All of a sudden he started itching his tail. I bathe him once every one or two weeks. I give him his flea and tick medicine the same time every month. He is up to date on his shots and every thing else. But I just don't understand why he start biting on his tail. It's like something is there for him to be scratching at it, but when I look there's no fleas, no nothing. HELP whats wrong.

is it the top side of his tail or the underneath he is trying to get at? if its the underneath, near his bottom, it could be his anal glands. if not check through his fur to see how his skin is, he may have a skin infection of some kind going on from something.

Mine started doing this and when I took her to the vet for a booster jab, the vet emptied the anal glands which were full and obviously causing irritation. Get the glands checked out (it's only a 1 minute job)
Also consider the food, as sometimes this can cause probs with the anal glands (which are apparently the dustbin for toxins in the system). A low protein/fat food and careful with feeding rates seems to be the way to go

if the poo is soft, this can cause the anal sacs to not empty, dogs need firm poos to stimulate them so you may need to look at the food they are having. mine are fed raw which can be high in protein but their poos are firm unless they have had a marrow bone, which can loosen them.