I think pregnancy tests are pretty accurate, so would guess that this is a hormonal blip. Shifts in hormones can alter when we get our period as does changes in routine, weight gain or loss, stress, illness, etc. If you were diagnosed with pcos, it would not be unusual to occasionally miss a period. You can check in with your doctor though. Hey, also . . . want to say great job on losing that weight and exercising! That's no easy task. So, that's absolutely fantastic!