I am a 24 year old, 2nd year law student. I am studying for exams: stressed + little sleep + lots of caffeine. My thumb keeps twitching! Is this norm?

No it's not norm. But neither is the context in which it is occurring. Respect your body. I think it is telling you that perhaps the coffee, lack of exercise, rest, and excelling in your grades, may not be as important as you might think. That being said I don't think your concerns warrant an immediate consultation. I wouldn't be surprised if a good massage to loosen your neck muscles would help!