Hello and thanks for your question. It is possible that this is a reaction to the amoxicillin. Usually drug reactions start within a few days of starting the medication and present with a rash. However, delayed reactions and itching are possible. I suggest that you take him to his pediatrician for an opinion and evaluation. It is important to determine if he is allergic to amoxicillin because it is a commonly used drug. If he is allergic a second exposure cause a more severe reaction. I hope he returns to good health soon.