692 days without a period

Doctors can't figure it out, I was put on birth control for this issue and I still haven't had a period after two months of being on the combo pill. I don't have a hormone Imbalance, I'm not pregnant, my iron levels are great, and when I got an ultrasound to look at my ovaries they seemed healthy. I've tried dieting to gain weight and exercising less (per doctors request) and that also didn't work. I feel defeated and I don't know what to do especially since the doctors just look at me and pretty much shrug now.

Any advice?