Amoxicillin

My little one just got diagnosed with an ear infection at his 4 month appointment. I gave him some amoxicillin for the first time last night and an hour later he was screaming bloody murder as I was trying to get him down for bed. I'm thinking maybe the amoxicillin upset his tummy? Is rhsy even a side effect? Anyone have a similar situation happen to them? I'm scared to give it to him again this morning