My 13 Year Old Son Has Been Sick With A

My 13 year old son has been sick with a virus for three weeks now. We went to the doctor a week ago and was diagnosised with a virus and an secondary sinus infection. He was put on an antibiotic then. He has been complaining of upset stomach since the beginging, but never having dirrahea or vomiting and also no fever. The stomach pain has only gotten worse and finally tonight he is complaining of sharper pains on his left side under ribs but above his stomach. Do I need to take him to the er? or wait and call family dr. in the morning?