Antibiotics and birth control

Two days after my period ended my boyfriend came in town and we had sex. I've been on birth control for 5 months now and I take it religiously (never missed a day) he comes inside me and I am never nervous about getting pregnant until now: three days after my period ended we had sex and he finished inside me. The next day I spent 4 days in the hospital due to a kidney infection (took my pills whole I was there) however I was told that my antibiotics could interfere and cause my birth control not to work, which worried me because there was no way I was able to get plan B or anything. I know sperm can live inside you for a few days... And it was the week I was ovulating that I spent in the hospital. Since then I've experienced bad cramps (not sure if due to medication or what) and now I feel sick to my stomach and have flu like symptoms on top of more cramps. My period is due in 5 days and I am