I think it is the heat and humidity if you don't have a/c. My Teddy holds off on eating when he knows he is going to go outdoors in the heat. When we come back inside and he cools off, he cleans his bowl. He also doesn't eat as much when his activity level decreases.
We praise and treat for trips to the piddle pad, so there are days when Teddy is bored and goes often and barely makes a dime size spot for attention.
Be careful not to overdo it with the cottage cheese, especially when it is hot.
If the pattern keeps up, I agree that a urinalysis is a good idea.