Period is late negative pregnancy test

Amanda

Looking for some insight. Long story short my cycle is typically very regular. I was taking oral birth control pills and got my period way earlier than expected while on the pil. My last period was over Christmas. Haven't had one since, and it's now a week later than it should be. I stopped taking the pill during my last period and have been extremely cautious not to get pregnant. I've tested twice both negative. What's the deal? Any input?