How do you avoid burnout

So I am working on a project for ~1.5 years now and I am already experiencing symptoms of burnout. I tried my best to take breaks/ reducing the work time whenever my body gave me the slightest hints of needing them. But maybe my breaks where to short or I didn’t manage to really let go enough. The thing is after a week of break I often feel the enthusiasm rise again wanting to jump back into the project. So that’s what I do, but if the break really is to short how long should I continue it ? How do I know when the break is enough ?

I would be super grateful if you could give me some advise or share your experiences regarding this issue.