i haven't read any of the answers just wanted to quickly say that my dd was the same, she used to SCREAM BLUE MURDER in the car and it was so so so upsetting, my parents and all my friends lived over an hour away and i used to absolutely dread the journey, it was so awful..... from about roughly five months though, it all stopped.... she would sleep or if awake would generally be happy.... so just wanted to say it IS a phase and he will get better.... at the time i used to stress about it so much but it passed and i hadn't thought of it until i read your post. also my dd is alot happier now that she is facing the front, they often get car sick when rear facing, but obviously its best not to turn them around until they are exceeding the weight limit for rear facing.

hang in there it will pass...

also i saw in toys r us this device that was like a toy but it attached to the backseat and it had a (safe) mirror so you can see bubs and bubs can see you, not sure if it would help but u never know, maybe seeing you would calm him??