L.K.
I, too had a son that hated the car. He scrreamed once he was strapped in! It also lasted untila bout 5 months.
We did change to a convertible seat pretty early thinking that was some of the problem. We had a Graco seat that got very hot - and he became sweaty. It releived it a little but he still would never sleep and was usually a bear.
So, he's better now and loves being able to see out the window. Maybe that was his problem???
Hang in there!