AF is late but still BFN

Crystal • 31 yrs old. 1st cycle TTC. AF is due 9/10 hoping so badly for a BFP!! My husband & I can`t wait to be 1st time parents!
So no sign of AF yet which is exciting but all 3 PT's were a BFN. This morning I took first response early detection too. Weird, AF is never late for me. Very regular 28 day cycle. Today is day 31. Anyone have this happen? Does it take awhile for PT to be positive? Thinking about doing blood test early next week if still no AF. Thoughts?