I have slight pain in my pelvic area. it hurts on the left side and it hurts to sit, get up and especially walk. what could cause this?

Pelvic pain: There are several possible causes -- it isn't possible to guess which one from only these symptoms. However, at your age -- and if you are sexually active -- an STD causing pelvic inflammatory disease PID) is high on the list of possibilities. Any and all cases of unexplained abdominal or pelvic pain need medical evaluation. See a doctor or clinic ASAP. Good luck.