Hey,
I dont know if this will help or not, but it sounds like something i had when i was about 10-14, and it turned out to be a kidney infection turned UTI/Bladder infection.
My doctor never diagnosed me, but told me it was appendix, then constipation, then AF pain, then possibly endometriosis, then i went to a different doctor, and she gave me antibiotics for a kidney infection, and it went away like that. I went to a specialist and she told me i could have abdominal migranes too, and to go to her when i got the pains again, so this was after my kidney infection diagnosis. Never had it again.

Im sorry if im wrong, but it really sounds like what i had.