Odd periods

I’m having a pretty weird time rn with my period. I’m 11-12 days late and the month before I had 2 periods. I’m 85% sure I have PCOS because my first gynecologist took an ultrasound (while I was on birth control mind you) and said there was a very very light case of it. I got tested again by another doctor (without the ultrasound and off birth control for for almost a year) and she said there was nothing abnormal. What else could it be or what could cause it? I’ve been tested for pregnancy and every singe one has been negative