Light period during ovulation cycle

I'm always TO THE DAY with my periods but this month I started a light flow (like my normal 4th day period) on the peak day of my ovulation cycle. This has never happened to me b4. I'm 10 days away from my reg scheduled period so too soon for a pregnancy test. Any thoughts?  Dr won't see me because it's "not abnormal to have off periods" however it is extremely abnormal for me. It has to continue a few more times b4 he will see me 😑. Any thoughts on what could cause it?