My son did the same thing for a while. I remember the first time we drove across town with no screaming (about 15 minutes in the car) I started to wonder if something was wrong.
We got one of those mirrors that you can hook to the back of the seat when the car seat is rear facing. He enjoyed looking at himself and also figured out that he could see me. The mirror was one of those Fisher Price ones with lights and music that I could turn on from a remote control. At first we used that feature a lot and then after a while it wasn't necessary. By the time he was about 4 months old he began to be OK in the car consistently.
Honestly, we didn't take him many places by car when he was that young so he was only in the car once or twice a week. When a friend had a similar issue with her older daughter, she made sure to take her younger daughter somewhere in the car at least 3 or 4 times a week so she would be used to being in the car at different times of day. More car trips may help too, if you haven't been going out much.
Good luck. You will all get through this stage.