What am I?

My last period start date was April 29th. I have not had one since then, and even then it only lasted 3 to 4 days. I have been having some lower backaches but all negative tests. Starting about two days ago my breast gave become a little bit tender around the nipples, and my drive for sex has went up extremely. I took a cheap dollar store test ( I am currently out of my home town on vacation) yesterday and it was still negative.... what do you guys think is going on? thanks for all comments in advance