R.J.
Appendicitis
Gas
Ulcer
Worms
Cancer
Potassium Deficiency
Inflamation of the _________ (pick an organ, protective sheath, or connective tissue, any organ, protective sheath or connective tissue)
Ovarian Cyst(s)
Endometriosis
Pregnancy
Slipped disc
Lower back injury
Pulled muscle
Flu
Mild case of food poisoning
Lactose Intolerance
STD
PID
PMDD
Off Cycle Period
The list, quite literally, goes on. Without an exam by a professional, there is no way to know.