Horrible crying in the car

Does anyone have any experience with a baby that cries as soon as they get in the car? My 8 month old son does this EVERY TIME. I put him in his carseat in the house and he's fine. Then as soon as I put him in the car and go to close the door he starts crying. He cries until we get to where we are going and even at that I have to take him out of the carseat before he stops. And today he wouldn't even let me put him in the shopping cart :( I really dont know what to do and I'm a single mom so I really REALLY could use some help.