Yup what LR said- its so hard to say!
Sometimes if your stressed(even if you dont "feel" stressed) it can muck AF up, especially when TTC, I had that happen once when TTC. Also, last month my AF was 4-5 days late as we had been sick that month with a horrid tummy bug and I was stressing about the late AF lol
I hope its good news for you though, fingers X'd for a BFP, like LR said, keep testing