HELP!!! . . . What is up with my mouse?

My mouse is my only pet and he gets lots of attention and effection. My mouse is a male, I am uming. He has the little penal pouch but, until now, has only had a bump where his testicles should be. Now they are getting bigger and he is acting crazy. He has started marking me by urinating on my shoulders or knees when I am handling him. He has been shaking/wagging his tail really fast, similar to a rattlesnake, when I am doing anything in his cage. Is this normal???? Is he going through mouse puberty or something??? . . . . If so, Is he going to get all wild and crazy, or will the crazy outbursts fade out??