Antibiotic allergic reaction?

I was prescribed to take an antibiotic for 10 days for bronchitis. I'm not sure what it was called but it started with a c. I started having weird symptoms while I was on it but didn't think much of it. I was getting bloody stools and my face was extremely red in my cheeks and across my nose. We called the doctors and they said to just keep an eye on it since I took it for all 10 days. My lower back has been hurting reallyy bad to the point that I want to cry. Should I be worried about this? Like should I go to the E.R. or will it just get better?