Why did I get my period exactly 2 weeks early?

I am taking birth control pills and am terrified of the idea of being pregnant. When I finished my original period, I had unprotected sex about 4 days once I ended my scheduled period. I usually am really care full and safe when it comes to sex. And exactly 2 weeks after my regular start date of my period, I started my unscheduled period. Is there a possibility of me being pregnant or am I just being paranoid?