My 3 Year Old Son Was Treated For Strep Throat

My 3 year old son was treated for strep throat last Saturday and has taken amoxicillin for 8 days. Yesterday and today he said his mouth hurt and threw up vomit. Took him to urgent care this evening and the N.P. Said his sinus could be affecting his stomach. He just woke up now crying saying he wants a bandaid for his stomach.