Oops, I meant unexplained infertility. Gosh, I wish we had unexplained fertility- we wouldve popped out a few babies by now.
My DH and I tried for three years on our own before seeing a specialist for help. Even after all the tests they did for both DH and I we had unexplained fertility. In the end I was placed on a regimen of increasing fertility hormones and lowering TSH. We were finally successful after nine months. If you're already a couple of years in with no luck I believe the next step would be to get a referral to a specialist. Good luck!!
Without seeing your doctor know one can know for sure. Be aware just cus he has kids doesn't mean everything is ok, he may still have a low sperm count.