Faint positive once, the rest negative

My last AF was august 3, due to start Sept 20. Tested the 21st with 3 different types 1 was positive, the rest negative. All tests since then have been negative. My doctors office said to wait to test for 2 weeks... it's been 2 weeks and still testing negative. And no AF. Does this sound like a chemical pregnancy? For anyone who has experienced one, what should I look out for. I'm just so sad. That was the only positive we have ever gotten.