Intense period help

Since getting my period back after my son was born in 2020, my periods have been on time or early with PMS being bloating and a headache and an ease-in flow. Super regular, no complaints. This month, I was 5 days late with negative tests, no PMS, and an immediately HEAVY, clotty flow that started last night. Today, I'm getting pelvic and back aches which isn't typical. Has anyone else experienced something like this before? Hubs and I are TTC, so while I don't think it could have been a chemical pregnancy due to the negative tests, I'm not sure.