24 yr old female abdomen below my belly button was tender to touch with some cramping for 2 days and is now gone what could it have been?

Multiple causes: Abdominal pain below belly button with cramping could be from gas or other gastric causes. Pain from Reflux disease is usually above belly and from menstruation/ovarian causes is a bit lower. If your bowel movements are regular U can try OTC antacids if it recurs and consult you physician for additional testing as indicated by physical examination.

Poss ruptured cyst.: If you are not on birth control, you get a follicle (ovulation) cyst every month. Sometimes that cyst will rupture and bleed internally, which can cause pain that can last a few days.