I had a "slump" this spring. After an injury, riding just didn't seem to be as much fun as it had in the last several years.
Then I realized that the biggest part of my problem was that I bored out of my mind. Riding the same route over and over was, I believe adding to my slump. So, a couple of weekends ago I rode with my daughter and son-in -law and let them pick a route, as long as it was new to me. And last weekend I sat down on Friday night and mapped out a solo ride for myself. It was nice to be looking at some new scenery for a while.
I'm still doing the same short, boring week night training rides but I'm also planning some more long and varied weekend rides to break up the monotony.
Give it a try.