Not pregnant, but absent period?

Madison

Hi y’all! So urine and blood pregnancy tests are negative but I had a one day period after my previous period was super light and I spotted in-between. Never experienced any of this in my life and I am 27 years old. Do any of y’all have any idea what could be going on? My thyroid levels are normal and everything else seems fine. I don’t know what to think. Need some insight!