Antibiotics and missed AF

I've been taking antibiotics prescribed by the doctor for the past three days, twice a day. Told her I was TCC and she said it was fine. Yesterday, I got major spotting, so I thought, ok! I'm out for this month. However, today, I have nothing; no cramps, no spotting. AF was due today for me, but it's completely on hold. I took a hpt on Tuesday and Wednesday and they were both BFN's. Could this be a side effect of the medication? Am I in for a very painful AF? :-x