Exhausted

My husband and I have been trying for a little over a year. Every month I feel as though I have the symptoms of pregnancy - and last month, I felt like I had them all...but I started my period. For the past 4 months I've been 7 days later than the last, but my ovulation never seems to be when the calculators predict. Ovulating Predictor Kits don't work at all. My basal body temperature never seems to have a real significant rise and fall. My doctor finds nothing wrong with me, and won't consider any action until we've been trying for 2 years. It seems every time I talk to someone, we find out someone is pregnant. My sister has been trying for 2 months longer than I have (she's 38, I'm 31) and she JUST got pregnant... since she and I were late, we both had the same period last month, and I was having the same symptoms she was, we got excited about being pregnant together. But no...she is, I'm not. Not that I'm not ecstatic for her, but I get so disappointed... I'm especially tired of hearing "When you stop thinking about it...you'll get pregnant." That frustrates me even more...How do I stop thinking about it?? Everywhere I go, someone asks me if we are pregnant yet. (Note to self, stop telling people you're trying to get pregnant...then they can't ask.) We're exhausted... but not giving up.