I have a sharp pain on my left lower abdomen. What's happening?

A variety of causes. Left lower quadrant pain in a 17 year old female can be due to a variety of causes, both gynecological, urological or gastrointestinal. If you have no intestinal symptoms, such as diarrhea, nausea or vomiting, it is less likely to be GI. Urological causes can be stones or urinary tract infection. Gynecological causes can be cysts, pregnancy, endometriosis, infection. See your PCP for input.