Am I pregnant?

I've been on birth control for 5 months now and have had unprotected sex with my boyfriend many times while on it. I've never experienced any problems, or scares, before. My period is unpredictable and I am never quite sure when I will be getting it. Last month it lasted for about 3 weeks so I don't know if I should be expecting it any time soon. Wednesday, April 6, was the last time my boyfriend and I had unprotected sex. Thursday, April 7, I stayed home sick from school with a sore throat and headache. I was supposed to start Bactrim that day, and was given one in the morning by my mom. Later in the day I realized that I had taken the antibiotic and that it decreases the effectiveness of birth control. I have not taken the antibiotic since, in fear that I could become pregnant. I am currently still sick with a cough, which is causing me abdominal pain so I am unsure if it is pain from the cough, or stomach pains that could mean pregnancy? Also, I started bleeding lightly the other day but sometimes it is a little heavier than spotting. I am unsure about all of this and was wondering if anyone could give me some insight. I plan on taking a test this Wednesday since it will be 2 weeks after the initial unprotected sec, but I have been stressing a lot lately.