Pregnant or body acting up?

I've been feeling extremely dizzy and nauseous for the past week at the point where I can't sit up or stand up because everything is moving so fast. I've also been cramping since my period ended. On October 3rd I got my period and the next day (4th) my SO and I had unprotected sex and he accidentally came in me. I'm on the pill but a week before that I've been on antibiotic for 3 days. Can I possibly be pregnant? or is my body acting up? I'm suppose to get my period the 31.