birth control and antibiotics??

I've had a kidney infection the last 2 weeks and I've been on antibiotics and I completely forgot that antibiotics cancels out your birth control😳 well me and my husband had unprotected sex the past 3 nights but i was on my period, but towards the end of it.. what are the chances I could be pregnant? We have a 1 year old boy right now, it was so hard for us to get pregnant with him cause I hardly ever had periods like maybe 1 every 2-3 months, so I'm not familiar with the possibilities of getting pregnant while on my period. I had to take chlomid to get pregnant with my son