I can totally relate to your situation because guess what, I nearly did the same thing. The first masters program I completed 2 years of required coursework but my student teaching component was stymied by my advisor who was, for lack of a better word, a horses behind, in that he refused to sign-off on the form that would have allowed me to student teach. He was mad at me for going to administration to complain about him, so he refused to sign. The academic dean of my program told me I would regret leaving before she made her decision. Well, hindsight is 20/20. I do regret it because I spent these past 3 years in the same masters program at a different university, hoping for a different outcome. Well I'll graduate with a masters degree finally but after wasting 3 extra years repeating the same coursework. Pretty dumb.

Don't quit your post-doc program if you're only 2 classes and your thesis. Yes, you're miserable because you are burnt out. Post-doc work is not a fun existence which is why most people either drop out early. At least you were smart enough the second time to do a completely different subject, which isn't what I did. You will feel so much better about yourself if you see this grad program through to the end.

I know it's hard to be away from your family and friends who are your support system too. Maybe you could take a semester off to go back home for 3 months. Spend that time with your family and friends who (if you have good relationships with them) will act as a temporary respite away from the stress of grad school. Or if that's not possible for you financially, then try to include some exercise time into your schedule. Whatever it may be. 5 minutes of walking each day, or whatever. Physical activity raises the body's Dopamine levels which improves the mood.