L.A.
Totally Normal!
Do not freak out.. Just be strong.. I bet what happens is when you drop him off, just a few minutes later he is just fine.
In the evenings, on the way home.. give him a healthy snack in the car.. When you get home.. play blocks or something with him for a little while..
Transitions of kids this age are difficult.. But they get through it.. The secret is to decide how each drop off and pick up is going to be.. and follow it..