Well this is weird...

Good afternoon everyone! So I'm kind of confused about what my lady parts are up to. I was supposed to be in full blown AF today but still nothing but a slight spotting. Dark brown. Very light. I've been PMSing and cramping like usual but still no flow?? I'm like clock work with my period and so this is a little weird for me. I've taken a couple of hpt but everything is negative. I don't think I've ever been late... EVER. Any thoughts??