I have unexplained infertility as well but was recently tested for an overactive immune system. The tests came back abnormal, so basically my immune system has been killing off the sperm and any potential developing embryos. I started on a new treatment this cycle... oral steroids (Prednisone) and an IV infusion of Intralipids. AF is due on Monday. I tested early... BFN. Will test again one last time tomorrow morning. Whether it turns out to be BFN or BFP, I'm positive this is what has been preventing us from getting pregnant and it will only be a matter of time, with God's help and this new treatment, before we get our miracle baby.
The tests for overactive immune system are expensive and probably not for everyone, but for me it has already been worth it! We are also going to do additional testing for DH if no BFP this cycle. We will do a DNA fragmentation test and some sort of enzyme binding test.