Boy 6 with urine infection take 250mg/5ml antibiotics after take pills start hurt stomach and vomiting. Can be the cause of antibiotics? To strong?

Possibly. Antibiotics commonly cause stomach upset. Sometimes taking them with a few crackers will help. Also make sure he is otherwise getting better. It may be that his UTI is getting worse. If he just can't tolerate the antibiotics review this with his doctor for another management plan. All the best.