Is there a chance I could be pregnant, or is my period just being weird?

I take a daily birth control pill around noon and have unprotected about once/twice a week with a guy I've been seeing, which never ends up with semen inside of me (it usually goes other places). My periods are not usually heavy or light, just average. A month ago, I barely had a period, it was super light. A little over a week ago, I forgot one pill but remembered to take it either that night or early the next day. The next day, I had a little breakthrough bleeding, enough to stain but not that much. So I took an extra birth control pill and a ton of advil to make it stop, and it did. About a week later it was time for me to go off my pill (for seven days, as instructed), but there was no bleeding. Once the week was up I went back on the pills again. It's only been a day since then, but I'm kinda worried because I missed it and the one before that was barely noticeable. Could I be pregnant? Being pregnant is the last thing I want. Today I bought a 2$ pregnancy test at a corner store but I'm not sure if it would be super accurate because it was so cheap, but surely they can't sell faulty pregnancy tests. What do you think? Thanks!