Missrae, you say that you've started exercising. Years ago, when I was slimmer (so nearer your build judging by your weight and height) and had a bit of a pot belly but was flatter above the waistline, I started swimming and developed exactly the kind of upper belly you're describing, very quickly. I think it's because I was developing those muscles so they started to protrude, but they were under a layer of fat so looked quite weird. When I got a bit fitter it flattened out fine
If you're doing exercise that's building up and strengthening your abdomen that may be what's caused this. It's like the top part of a six pack emerging!
I do have PCOS as well, diagnosed 18 years ago, but ten years ago I had a completely flat stomach after being at least 30lb overweight a few years before so it can be done! If only I'd appreciated then what I had...
You're doing brilliantly, I really admire you for how much weight you've lost.