possibly pregnant?

I am supposed to start AF on friday and I am currently 13dpo. I have been cramping during the ttw. My boobs have become more sore over the week and my nipples are actually a little tender. They arent extremely sensitive but if touched it hurts a little. I have taken 4 hpts one at 6dpo one at 7 one at 9 and one at 10dpo and all were negative. I now am just waiting to see if my AF shows up. Is it possible to be pregnant and just not have enough of the hormones to actually end up with a bfp?? im just trying not to get my hopes up.