Pregnant or Something Else?

So about two and a half weeks ago I had sex with my guy friend with benefits. We used a condom mostly, but there was a moment when we didn't use one. He pulled out but I still was worried so the next morning I took Plan B and went back on my birth control. Ever since then I've been having light stomach discomfort almost every morning that usually leads to a bowel movement, and then I'm fine for the rest of the day. I've had very mild/light nausea a couple of days, but no breast tenderness, extra fatigue, or weird cravings (although a few foods have been turning me off lately. But I wasn't necessarily crazy about those foods before anyways). I haven't been cramping, but I did notice PMSing around the normal time right before my period. According to my calendar I should have started my period this week, and I feel like it's on but I haven't actually had any bleeding, just some clear discharge. But considering I started the pill again a week later than normally and I took the Plan B, could my symptoms just be due to a high level of progesterone? I'm scared to take a pregnancy test because that makes it feel more serious. Help!