Can amoxycillin be bad for my liver or cause stomach ulcers?

Yes: Potential adverse effects on the liver by Amoxicillin include acute cytolytic hepatitis with a resulting increase in serum transaminases (ast and alt); cholestatic jaundice; and hepatic cholestasis. Although there are some GI side effects, such as nausea, vomiting, and diarrhea; a short course of Amoxicillin or Augmentin (amoxicillin and clavulanate) should not cause peptic ulcer disease.