Pain in my pelvic area, lower abdomen?

I am a 20 year old female and have been experiencing pain in my pelvic area (mostly on the left side) and lower abdomen. Yes, I am ually active. The pain really kicks in with sudden movement or when i cough or sneeze, but other than that I normally don't feel it much unless its sudden and doesn't last long. Things like standing up really fast make it hurt. Its not an intense pain, but is uncomfortable. Kinda feels like someone is pushing on me. Any idea what this could be? I am not on any medication and have no history of any stomach problems.