I don't have alot of advise but just wanted to say I am thinking of you and praying that your next sticky BFP is just around the corner. It seems a fairly common scenario when I was ttc my 3rd. Many of us had not had trouble in the past and suddenly it wasn't working the next time. Out of over 20 of the girls I become close within several forums not just this one almost all have gone on to get pregnant and have a baby and some are now pregnant with another conceived much easier then the last time. We all took over the 2years to conceive our babies. Sadly one have not yet.
Have you had a laparoscopy? This is what diagnosed my problem which would never have been known without it. I'm surprised at the amount of woman who have had every test but not this. What about a biopsy to test for natural killer cells?