Rocky, that maternal thing is taking over again, and I'm wanting to make sure that you're okay!
I agree with
@jaylach - Please tell your doctor, in private if you're self-conscious about it and don't want your parents to know. I know you said that it doesn't effect you too much, but since you don't know the underlying cause, and you feel a need to hide it, it's really worth getting checked out by someone qualified, you know? If it turns out to be a mild form of tourettes, some weird muscle thing that doesn't cause many problems, or some other minor, non-harmful thing, then great! But if there were some more serious underlying cause, then it's always better to be diagnosed and treated sooner rather than later.
Not trying to alarm you or anything! Not suggesting that it is something serious, or that it's something completely harmless. I'm not medically qualified to know, and neither are you... but that you feel the need to hide it, is that because it makes you self conscious perhaps? Or you don't want to see a doctor about it, and your folks would make you?