no sign of af, bfn 😕 HELP !! 😩😭

AF was due Saturday 5/21, before all of this I had af like cramps from 9 or 10 dpo up until Thursday 5/19 they stopped, since Friday 5/20 I've had a lot of creamy/watery cervical mucus, it's so much that it makes me think that my period has started and I have to keep running back and forth to the barroom to check but nothing, I took a test this morning with fmu at 15dpo and bfn . period is a day late . how long should I wait until testing again ? has this happened to anyone and you still gotten a BFP? if so what dpo past your AF date were you ?