I have had this problem for awhile now and I have no idea what it is. Whenever I get nervous or feel like all the attention is on me, like speaking in front of a class, my head will twich or shake. I think it may have something to do with anxiety but I'm not sure

haha, yeah, sounds like anxiety to me. I had a teacher who's head would constantly twitch when she made mistakes up on the board. I'm not sure how bad your twitch is, but BELIEVE me, it can't be as bad as she was. I'm just amazed her head didn't snap off.
As for me, my eyelid twitched when giving presentations. After I took a public speaking class the twitch went away since I was used to talking in front of people. I still get it occasionally when upset or frusterated.