To begin with, I'm on birth control and therefore have a normal 28 day cycle with my period lasting usually Wednesday to the following Sunday (just for reference, I started on Feb. 10th). The last official day of my period was Sunday, February 14th to which I started taking my birth control pill again (same time every day). The following Tuesday, the 16th (it's at the point where it's tapering off and now I have that brown discharge), my fiance and I had sex. Now, he stuck it in for a few seconds, possibly a minute or two but definitely not longer, and then he pulled out, put a condom on and finished. For about half a week now I've had a mild lower back ache such as like the aching you experience right before starting your period. I'm just really concerned if I could be pregnant or not? Also just for a few more facts, we had gone bowling 2 days in a row (that Thursday and Friday, two hours each night) and were going hardcore so we could get in as many games as possible. The point of that extra info is that I've pulled my back before while bowling, so I'm just wondering if that could be an answer to the back aches... or could I just be imagining all this because I'm stressed out about the situation? Thank you for taking time to answer and help me!