It could be a range of things:it could be an ovarian inflamation, possibly (not not likely) a kidney infection, and then there are the other more serious issues. Again, I would encourage you to immediately see your GP. If the pain cannot be arrested with acid blockers, you may be scheduled for an endoscopy, where a small tube would be inserted through your mouth, into your stomach, where the doctor can examine your stomach. It's fast and painless, although it can initially be a bit bothersome. Please, however, no one here can triage based upon such limited information and the absence of a history. Please do contact your GP today for an appointment.
I wish you well
Fr Bill