My boyfriend and I had unprotected sex twice in the course of 24 hours (came in me twice) and I then found out I had a UTI three days later. The nurse prescribed me nitrofurantoin twice daily for a week. On the third day or so I had bouts of brown discharge that resembled menstrual blood but I wasn't supposed to have my period till the following week. I'm on the pill; so far it has been 5 days of the placebo and I haven't bled. Is it possible I got my period early because of the antibiotic, or that the antibiotic delayed it? I've had some cramping lately but no bleeding still. I take my pills every day but not always at the same time. Please help, I really can't afford to be pregnant.