Can I be?

Ive been on birth control for approximately five months now and have taken it as directed. My boyfriend and I have unprotected sex (well not really sex but he put his dick inside of me like twice) 4 weeks (give or take) ago. I'm having constipation and kinda moody but I usually am emotional in general. Could I be preggers? And a heads up I eat crappy food like junk food and don't exercise regularly if that has to do with my constipation problem. A little bit of sore back but I'm thinking that's from my backpack...what do you guys think?