Pregnant?

I'm engaged. I'm also on birth control, and going to start my second semester of university in january. But I'm really scared. I think I'm late on my period but I'm not sure, because I spotted at the time I should have had it. I'm also having like a sore tender pain in my right boob when i touch. just my right boob. it's a bit farther back but above all its in that little hollow space behind my nipple. I know that sore boobs is a symptom of pregnancy, but my doctor warned me that a pain like that could also be breast cancer.

any advice?

UPDATE...

not pregnant.... now all I need to do is make a doctors appointment. yay. I'll update as soon as I find out more.