Antibiotic And Taking the Pill

Hey there, I was just wondering if there is a chance that I could get pregnant. I recently took my pill for the full month and took it everyday at the same time, half way through the month I got bronchitis a week before the doc put me on my meds (biaxin) my fiance and I had sex. I was still on the pill but the antibiotics weaken the pills affect? Can it still have affected me even though it was the next week I started taking the antibiotics?

Say for instance still being on the pill we had sex on wed. And the next tuesday I started to take the antibiotics is there anyway of getting pregnant?