First, I recommend talking to him to see if anything has happened/changed. It could be your child doesn't like a new staff member. Also, check with the licensing agency to see if there have been any complaints.
True Story: My sister went through the same thing with 3 of her kids. Suddenly, they didn't like their homebased sitter and they wouldn't say why. A surprise visit by the licensing agency revealed that the kids were being locked outside during the day and let in only for lunch and to use bathroom. My sister freaked and felt guilty for the longest time. She eventually found a great lady that she stayed with for years.
I'm really glad you noticed your child's behavior and are seeking out advice.