I've been experiencing a lot of stress since becoming sexually active so maybe that is also contributing to my period being late. Can pregnancy definitely be ruled out as a possibility?

I am an eighteen year old female who began taking birth control ( Lo Loestrin Fe) on October 17th, 2016. Since then I have taken it at 7:00 pm each day, except for two occasions where I was twenty minutes late. My last period was November 20th, 2016 and shortly after its completion is when I had sex...