I'm 18 and i'm on birth control. my left leg for my knee up hurts and keeps going numb. should i be worried? this has been going on for about 4 days.

See a physician : Although this could be as simple of a so called " pinched nerve" , but it can also be due to a "clot". Because of birth control. See a physician ( neurologist , internist or your family physicinan ) asap, or go to er.

Possible blood clot: I would vcertainly recommend that you be evaluated for a possible 'blood clot in your leg. While rare, this can cause pain and numbness in your leg. Other than that it could be a local nerve irritation.