If you run across many drafts of your own and the ‘joy’ is drained out of you, then, it’s time to think about what exactly is causing you to feel that way.
If the changes you’re making don’t make the story better, stop and put it away for a while (a week? a month?).
If you’re having trouble deleting certain scenes, stop and put it aside.
Maybe a second opinion other than your own will open your eyes. I know I have taken scenes out of my novel to keep the pace and plot consistent after hearing others give me feedback.
If it doesn’t move the story along, discard it.
If you love the story, put it away and get to other writing. Maybe something will click while working on something else to get you back on track.
The main thing is that you keep writing in some way.