I was once in sort-of your situation but I hated my job a little less and I didn't build a side project. I switched to a different team in that company -- to so

I was once in sort-of your situation but I hated my job a little less and I didn't build a side project. I switched to a different team in that company -- to something both new to me and less stressful than my old team. It was a world of difference and made it much more bearable. You should definitely try it. (I did eventually quit anyway after fully vesting.)