I had a longer road conceiving and maintaining pregnancy with this one. I think part of it was me being a few years older (it's just a different game in your 30's versus your 20's for some of us), part of it might have been related to some medications I was taking, and part of it was just luck of the draw. It ended up taking me a little over a year to achieve a sticky pregnancy, using OPKs and such, which I hadn't needed to previously. I was never a "pregnant on the first try" person, but it wasn't something I had to wait for very long. I understand how frustrating it can be.
For me, I was taking melatonin when I was first trying, which I later learned can interfere with fertility. I also often took ibuprofen, which, again, can interfere with implantation. I definitely recommend reflecting on all your meds, OTC and otherwise, and any other lifestyle differences from when you've become pregnant before.
Good luck to you and your partner.
M/C at 8 weeks -- May 2000. DS #1 -- March 2001. DS #2 -- November 2002. (Ten year break!) DD -- October 2011. M/C at 8 weeks -- May 2013. Expecting #4 late July.