If you're seeing a therapist, this would be a good thing to work on. Yes, talk with your doctor and discuss what to do with the testosterone. But, unless you want to stop for good, it sounds like this is something you're going to have to figure out how to deal with sooner or later.
In my experience, the basic trick to dealing with unpleasant or destructive emotions is not to try and change them-- it's just not to let them rule you. Notice the anger, acknowledge it, even express it if there's someone, like your girlfriend, who needs to know how you're feeling. If you're feeling agitated or violent, have something to do to work off that energy-- exercise, loud music, video games, whatever works for you. (But if you get to the point where you're actually striking out physically, against people or objects, you *definitely* need to work on it with a therapist.) But instead of trying to control the emotion, just control your actions. The anger will pass on its own, especially if it's out of proportion to whatever provoked it.
