I thought birth control pills arent 100% until after the third month taking them? course its been quite a few years since I've taken them and things may have changed.
I've heard of false negatives, but rarely false positive if done correctly. If pills arent taken correctly-they can cause problems and wacky periods. I'm with everyone else, check with your doctor. In the mean time, treat your body as if it were pregnant and try not to worry.