my son - is he allergic?

this is the second time that my 13 month old son has received penicillin based antibiotics he was sick violently for 10 days consecutively whist on the medication and a few days after last time however, we assumed it was part of the virus, he has today had some amoxicillin for a chest infection at 6pm by 8pm he was violently sick just as before is there a chance the antibiotic is causing this?