Hello
Thanks for posting your query at DoctorSpring.com
I can understand your concern.
From the history that you provided, it seems to be a drug reaction that he seems to be having after taking amoxicillin. I would recommend that you stop the amoxicillin and visit your doctor immediately.
Meanwhile he can take an anti allergic tablet like tab. Allegra 180 mg one a day. And apply calamine lotion over the affected areas.
Hives in this case are drug induced, they can even progress at times to cause a severe drug reaction. Hence its better to visit your doctor immediately so a proper course of treatment can be started.
Please let me know if you have any queries.
Take care