Impossible to conceive.

My fiancé and I have been trying to get pregnant for almost 6 years now. We've had one miscarriage. I've tried tracking my bbt, taking prenatals, ovulation kits, everything except see a fertility doctor. Nothing seems to help. Right now my period is 3 weeks late and I've taken two pregnancy tests and they both said negative. I'm just so depressed because all we want is to start our family. Everyone around us is and we just seem to have no luck. Does anyone have any suggestions to help us conceive quicker?