Confused 😕

OK so here's my situation... Af was due on September 12th. I had slight brown discharge last night with cramps and back pain (7dys late). This morning I get up and Af is there heavier than ever. I only have slight cramping n back pain. But my flow was extremely heavy and steady with slight clotting (I normally can just wear a Panty liner but I had to wear a pad today). My period has never come this late in the month. I took hpt and blood test about a week ago and came back BFN. Has this happened to anyone else!? Is this normal!?