Where did AF go?

I was holding off to write about this because I figured it would come. I was due for AF on the 15th/16th of August. I am an extremely regular person and always get it when I'm supposed to, and I have not missed a period in 10 years (I'm 20, btw). Either a day or two before I was supposed to get AF, I noticed what looked like a spotting of redish-pink blood. I had it for maybe a couple of hours, then it went away. Never got AF. I am now about 8 days late. For the entire past week I have been very, very nauseous all the time. I've had some cramps, but they are nothing like my horrible menstrual cramps that I'm used to. In addition, my nipples are driving me nuts with the sensitivity, I pee every hour and I feel constantly bloated. It feels like AF will be here any minute, but she never comes. I have no idea what this could be, but pregnancy has crossed my mind, even though I've gotten two negative tests, one of which I took this morning. Any advice or previous similarities would be greatly appreciated! Thanks :]