There are several resources that have ministered to me whenever I've experienced homeschool burn out, and I'm just certain I can't do better than to direct you toward them.
The first is a series written by Craig and Barbara Smith entitled Keeping Going When the Going Gets Tough. Craig and Barbara are dear friends of ours who live and homeschool their children in New Zealand, where they also serve as the directors of the Home Education Foundation. We have learned countless many things from Craig and Barbara, not the least of which is their gracious and godly example of adopting several young siblings while their own children were already in or fast approaching adulthood. At a time when most empty-nesters are planning how to indulge themselves in their retirement years, Craig and Barbara took seriously the Biblical definition of "pure religion"- to care for widows and orphans.
The other equally encouraging resource is a chapter devoted entirely to the subject of homeschool burn out in Elizabeth Foss's essential book, Real Learning: Education in the Heart of the Home. This one chapter is worth the price of the book.