So, you can get pregnant any time you have unprotected sex. You may not know exactly when you will start ovulating again after taking birth control ( you not ovulate on birth control. The hormones prevent that and you only have any bleeding because during the 'off week/sugar pill week' hormones aren't going in so you will have what looks like a period. It's really only spotting as you never ovulated). It normally doesn't start up immediately though (ovulation). However, women are irregular. You probably had the same kind of spotting you get during the off week of pills initially. And your hormones are normalizing after being manipulated by the pill. Are you pregnant? Probably not. However, going back to my first statement, any time you have unprotected sex and are not using birth control, you are risking pregnancy. Wait 2.5 weeks after your last unprotected sex and take a pregnancy test. I'd fully expect it to be negative but you have to rule it out. Right after coming off the pill is a time in which your cycle is less predictable for what is really happening. So, use a condom until you have regular periods again.