antibiotics and birth control. OH NO.

I have been on birth control for 2 months.
The same time I started my birth control, I started minocycline for acne.
My boyfriend and I started having sex without a condom about 3-4 weeks ago, probably close to every other day. He always pulled out untill 2 weeks ago when I was on my period, and since then we havent gone back to puling out.
I woke up this morning and realized that my mom always said 'remember to take your antibiotic' constantly at night. I remember when I was on birth control when I was younger the doctor telling me about how the birth control is less efective with an antibiotic.
Is there a major chance I am pregnant?
My boobs are terribly sore, and I am having wierd abdominal cramps, almost like right before your period.
I was thinking maybe the boobs being sore was just from the birth control, but is it possible that the birth control was never really effective since I started that and the minocycline at the same time?
I'm only 17.

any advice anyone?