I Have Been On Birth Control For About 5 Years

I have been on birth control for about 5 years now. had my period lighter than normal and took my next pill for the following pack later sunday night and had sex that morning. Now I am feeling weird sensations in my abdomen area. I've been slighty constipated but nothing to grab my attention more than these weird butterfly sensations in my abdomen. Should I be worried if I am pregnant?