Not sure if this is the right topic board. Apologies if not.
Background: TTC for 5 years; undergone numerous fertility tests and diagnosis is "unexplained infertility".
Cycle length is 26 days - regular as clockwork & never miss a period. Positive OPK (I test every month) is always CD11/12 so no issues with irregular cycles or ovulation.
I'm currently on CD31 which is just unheard of for me with no AF. I took a pregnancy test on CD28 which was a BFN, so waited until this morning and again...BFN. 
I've got painful cramps and have had them for days; but just no sign of AF.
Anyone experienced this? I'll obviously go to the doctor if this continues but just looking for some advice/thoughts before that.
I was so convinced this month could be it when I was late, so to see two BFN is SO gutting!!