Going back to your thyroid levels did they measure T3 and T4 individually? Sometimes a thyroid test just covers the basic TSH level. That doesn't cover everything. There are many women that are depressed with her thyroid test comes back low normal and regular doctor will not treated sometimes you might need a little bit of Synthroid it's really a call that An endocrinologist has to make or ur pd if they know that area. It's worth reading about.

I've also asked for a D vitamin test and a B 12 test mine were both low. That can cause problems of sluggishness for depression. It's just another base that you can get covered. Now my PD is looking into hormone levels. I'm not thrilled about it but it's just something else to rule out. I think you have to be your own health advocate.
I know I have severe depression, but my PD likes to cover all his bases. Yes sometimes it does come down to neurotransmitters or as I would say bum genes. Wish you best of luck!