I was in the same burnout boat. I took a month long vacation out of the country and when I came back I felt more energized for a total of 2 weeks. After the 2 weeks, it was back to feeling burned out and really just unhappy. I kept working and figured it was just a phase. It wasn't.

I quit my job last month. We'll see how I feel in 6 months. Hopefully, that was the cause! :)