What's going on??!

My last period was and has always stated on the 11th of every month. I haven't gotten mine for this month and I'm kinda worried. I'm 2 weeks late, my nipples are sore to the touch and my breasts not only feel full, but they hurt if i was to lightly touch it. Ive had cramping but no blood, white, milky discharge and ive been tired a lot lately from just simple activities, and last night i was hungry but i felt horrible nausea but no vomiting so today I bought a pregnancy test from the 99 cent store. A friend of mine who's on her third child told me it doesn't matter where you get it from and that even cheap ones work so i went that route. Lol But it was negative. Does that mean I'm testing too early? Am I pregnant? How do I know how any weeks I am?