Could you have been ovulating? Sometimes that can cause a LOT of pain if you have ovarian cysts. It can be anywhere on the spectrum to kinda uncomfortable to can't move and think you're dying. I almost had to call an ambulance once because I felt like even the movement of breathing was like being stabbed. I've also had it mildly where it's just this quite painful sharp pain on one side, but doesn't make me not functional. It's kind of frightening feeling, like you think something horrible must be wrong. I thought appendicitis too the first time I had that happen. Obviously it's only on one side and in the lower abdomen. If you're not near your period, that could easily be it. Basically if you are a woman of childbearing age with pain on one side not accompanied by a high fever, doctors will assume that's what it is, since the test for it is fairly invasive (a vaginal ultrasound) and often inconclusive.