My period lasted 1 day of heavy bleeding, then I got brownish spotting, now nothing. Can I be pregnant?

I took a prego test, it came out negative. I haven't had in two weeks, and even then it was once, and lasted only seconds as his rommy walked in and killed the mood. Before that, we haven't even seen eachother in weeks due to school schedule and midterms. My boyfriend always uses a condom, and as double measure pulls out before anything happens (so its not really enjoyable for me, infact my batteries are more pleasurable). I'm on my fourth month of the pills... Is it possible I'm pregnant? Or would the pills be affecting it? I can't be pregnant, it took me 4 years to get back to school... I can't afford a kid.... can it be stress? is there something else that can get this to happen?