Im feeling a mild pain on my left pelvic area & i know its not inguinal hernia since i have been ultrasound before. what could it possibly be?

See a doctor: An ultrasound may not see a hernia, especially if it was a pelvic ultrasound. Need to see a doctor for a physical exam to check for a hernia or other causes of discomforts.

Many things: It clear that an ultrasound and even physical examination can miss a small or occult hernia. The only way to diagnose these may be a surgical procedure, obviously a last teaort. The pain could also be from a muscle strain or a gyn related problem such as ovarian cyst, endometriosis, and even ovulation, called mittelschmirtz. If its mild, probably ok to observe. Check w/ your doctor to be sure.