Is it normal to have SEVERE adominal pain ?

My 31 year old daughter hasd been prescribed 500 mg of Erybid every 12 hours for a throat infection,infection in both ears plus a sinis infection. She was told not to take any food but to drink 1 full glass of water with the pill. After 3 days she is still suffering extreme stomach pain almost until the time to take next pill.

Is this normal??? Her husband did speak to chemist at drug store 7 he says she should eat just prior to taking the medicine.

Any advise/ suggestions.

Thank you