a little confused

So I'm taking a new birth control after the last one I was taking turned me into a holy terror. This one that I'm taking now is a lower dosage and makes me a normal person. I'm currently in the second month of my new pills, and I'm about 15 days away from my period. However, my boyfriend and I did the deed, and he came in me without a condom. We are used to doing this and nothing going wrong. But I'm getting weird cramping that I wouldn't usually see until at most week before my period starting. This is weird because I take the pill religiously and NEVER miss it. I don't believe that I'm pregnant because I'm extremely careful and I'm not seeing any pregnancy symptoms. Could it just be the new birth control?