Where does your stomach hurt? Is it upper right quadrant pain? Take your fingers and push in directly below your ribs to the right of your naval. If you feel a sharp pain there, that is your liver.
If you are also experiencing nasea, those are symptoms of hepatitis (drug induced hepatitis in your case).
Not trying to alarm you, but make sure this is not something more serious than some stomach upset.
Watch for these additional signs:
Dark urine and pale or clay colored stools
Loss of appetite
Fatigue
Abdominal pain or distention
General itching
Jaundice (yellowing of the skin or the whites of the eyes)
Nausea and vomiting
Low grade fever
Weight loss