Day 41 In cycle, no period, negative hpt.

Hi, I am at day 41 In my cycle, I have missed my period and have taken 3 hpt, all negative. I went to my doc a 4 days ago, negative urine test and blood test. The next day I had just a little spot of light pink in my undies. I haven't had anything since other than light cramping which basically happens everyday. Can anyone help? I usually have regular periods but just came off the pill in July 2015.