Well coming off birth control CAN mess up your period for a few months. With me not being on birth control anymore, my periods are no longer normal. Sometimes light sometimes heavy, and seldom on the same day. You COULD be pregnant though. I would take a test to find out.
You could be. Have you taken a test? If not you should or you could wait another week just to be sure. Sometimes are bodies are really funny and like to freak us out. I know mine does it to me every once in awhile. Here is one thing you could asking yourself. Any added stress or diet changes. Your 17 and there could be a lot of different things. Are you in any sports or after school activities? Maybe just the change in your schedule. good luck and keep us posted.