How long will the effects of an allergy to amoxicillin

Patient: How long will the effects of an allergy to amoxicillin last? My son took 2 pills, the last being Tuesday am, and he is vomiting and has stomach pain today. Went to a doctor yesterday, and that doc said that it should be better today. It’s not better, but not worse. My son is miserable. Is there anything that will help?

Doctor: