I'm not a person who usually has bad reactions to antibiotics but...

I'm not a person who usually has bad reactions to antibiotics but I've never been so miserable as I was taking this drug. I felt excruciating pain in my stomach all day, every day, while taking this medicine. I stopped taking it almost a week ago and I still feel like I have a big lump in my throat making it very painful to swallow. And the worst part is that it was prescribed to me "just in case", so I didn't even have to be taking it. Luckily as soon as my bloodwork came back negative for any bacterial infection things, they let me stop taking it, but like I said, I still feel ill and my throat is killing me.