Could I be pregnant or is it something else?

I'm 18 years old and I just got off the depo provera birth control back in January. My periods started the following month and they seemed pretty regular but the doctor told me they can be irregular for the next 6 months to a year. Well I have kept track of my menstrual cycle and on my most fertile days I used condoms. But now my period hasn't come yet. I had all my menstrual symptoms when I was supposed to start but no bleeding. I took a pregnancy test about a week after my scheduled period date and it said negative. A couple days after that I noticed a lot of this cottage cheese looking stuff coming out. What's wrong with me?