I missed my period. What's the possibility of getting pregnant?

[bisenchanted]

So about a week ago, the day my period was supposed to start, I received and preformed oral sex on my boyfriend. No ejaculate came anywhere near my vagina, yet I still haven't gotten my period. No drastic changes have occurred in my life to make stress a reason for my late period. But, we're both naturally paranoid and we're getting pretty stressed about the possibility of me being pregnant. I'm a virgin, and plan on staying so for a few more years. What is the possibility of me being pregnant? Is this just a late period? My periods have been pretty consistent, but February made my period change from the 21th-28th of the month to the 1st-7th of the month. Is this just another change in my cycle or is it someonething worse? Should I purchase a pregnancy test to ease the anxiety? Thank you.