What causes late periods but negative tests?

I know I should call a doctor and I will but I know it’s also way too early for them to see anything on an ultrasound. I’m looking for others who may have experienced the same thing? I’m a week late for my period but have gotten negative pregnancy tests, about 6 of them lol. But I’ve been having pregnancy symptoms worse than I’ve ever experienced since before I even missed my period. I’m talking like I can’t even function tired by 5pm, nausea all day, bloat all day, and itchy skin since a week before I missed my period. I’ve had one live birth and two miscarriages, every time I’ve gotten a positive test before I missed my period. What is going on???