I wrestled with this same question. Technically September 2012 was when we started NTNP and then when that hadn't produced a BFP we started actually trying (OPKs, timed intercourse, etc.) in February 2013. By December 2013 I was just devastated. I should mention here that both hubs and I are very healthy, have normal BMIs, don't smoke, don't drink that much, eat a relatively healthy diet, etc. My cycles were textbook regular and ovulation was always textbook predictable. When I started my period on Christmas Day (Merry Fing Christmas) I had a little breakdown and my husband made the executive decision that we were going to call and inquire about testing when we got home. I always had a gut feeling that it would be difficult for me to get pregnant, but I never guessed that after 19 months I wouldn't have a BFP. Fast forward to March 7th. All tests were complete and we went in to meet with the RE to discuss the results and were completely blindsided. Hubs' semen analysis was perfect in all areas but my results were unexpected. Without going into all of the details, I have the ovaries of a woman who is is 15 years older than I am (I'm 32) and my chances of getting pregnant without IVF are almost nonexistent and my chances of getting pregnant with IVF aren't that great either.
So what I'm saying is get tested sooner rather than later. Trust your gut. I hope I didn't scare you with my story, and I really am an anomaly, so I'm sure your results won't be nearly as bad as mine, but I think you owe it to yourself to get answers. Even if the answer is "we can't find a reason that you're not pregnant already," at least you will know that it's possible, and that will put your mind at ease.
Fingers crossed for you!