Why am I late??

I'm on CD 31 my normal CD are 29/30 I'm usually very regular. I've been trying to conceive since June I got pregnant in oct. and I had a miscarrage on November 20th 2015 at 6 weeks. I track my cervix and for the last week or so it's been SO high and extremely soft. I then had a regular period 12/21/15 now I'm still waiting for my cycle. I took ovulation tests and they went from dark to light so I assume I ovulated I took them pretty late in my cycle the top one was taken 1/6/15 then everyday after that until it got light and I stopped. I've taken a few pregnancy tests and they appear to be negative so why am I late??