What's going on with Regan???

Let's start with Friday. I took Regan to school and everythign was going well until Mrs. Jinks called him to get in line. He threw himself on me and Mrs. Jinks had to pull him off me and carry him to class. Then Monday night he did the same thing and Sean had to pry him off me and he also did it again on Tuesday at school. Mrs. Jinks again had to carry him to class. I have no idea what could be bothering him. It isn't the kids in his class because everyone plays together.

Look at this cute little face!! He looks so happy in this picture. Any ideas on what I could do?? I spent friday night and half of Sunday with just him. We went to Chuck-e-cheeses on Sunday for a b-day party and he was happy with that. I just don't know what else to do.