What Causes Headaches And Nausea While On Antibiotics For Throat Infection?

Hello, I had a very sore throat so my doctor prescribed a course of antibiotics (amoxicilline) From the moment I started to take them I started to feel dizzy and sick. I have now been off them for 1 and a half days and I am still laid out with headache and feeling neuseated. I am also struggling to eat anything. What should I do?