I used to get really bad stomach pains from about 4 years old and still get them now. I was in and out of hospital when I was little because of the pain.

Turns out when I get a sore throat instead of the glands in my throat swelling up, my glands in my groin swell up. Its really painful.
They thought for some bizarre reason that it'd stop after I had my appendix out at 10 years old. But, it didn't.

Good luck finding out. Hope you find some answers.