3 days late, brown spotting BFN

Normally I am pretty regular. I know when AF is coming like clockwork. This month is different. I had some mild cramp like sensations that started about a week before AF was due. Friday comes and there is slight dark brown spotting. Ok, it looks like it’s on her way. Usually will wake up to AF in full force. Nope. Yesterday it almost disappears and this morning is very slimy brown spotting. Tested and BFN. Has this happened to anyone else? I want to wait until Wednesday to test again if AF doesn’t come. Just worried it could be something bad. All advice is welcome. Thank you.