I guess it happens to most people. I get burned out, or maybe I should say discouraged at times when I was working on my daughter's single bed quilt. I just finished quilting it and it took me three years. In between those years, I was struggling to learn MQ and very "afraid" to do it on the real thing. I think I left it aside for one year before I came back to it. Hence I started on smaller projects eg christmas quilts in between. For the past six months, I was very focused in finishing that quilt as it's something I promised my daughter since three years ago.
It helps to take a break and do other things you enjoy. Or start a few other projects in between. You can always come back to your current project another time. Sometimes it's the process that tires us out. Especially when we stare at the large quilt and keep wondering when it could all be completed.