Hi, very confused.

I had my last period on the 11th of December, 7 days after ovulation I started spotting which turned into a light flow and lasted on and off for 6 days. My period was due the 18th of January and I still have not got it.
I have have had back aches, head aches, nausea at times and am more tired than usual. Also I have some pelvic and lower abdo discomfort along with an increase in milky white discharge, pregnancy test was negative at 5 days past expected period and have not tested since. I have had blood taken and ultrasound and both were clear for infection, PCOS, and any ovary or hormonal issues. I have two children already and feel I am pregnant, but like I said HPT was negative on several occasions with the last being over 5 days ago