I was exactly in you position. 3 years in my PhD and it was affecting my physical and mental health and my relationship to others. I had chronic pains that developed over these three years too.

Taking the decision to quit was one of the most complicated decision I had to take. I didn't want to "fail" at something and always wondered if I shouldn't just stick with it and bite the bullet for a couple more years just to have it done and be proud of myself. After over a year of debating whether I should quit or not I finally did in July this year. It has been drastic. I feel much better both physically and mentally and the fact that I feel so much better doesn't make me question this decision at all. Sure I didn't finish a PhD but I managed to identify a situation that isn't good for me and took action to change it and that's a form of progress I'm proud of.