I had the same problem with my baby when he was about 4 weeks old he decided that he didn;t like the car seat anymore and screamed, sometimes even before we got to the end of the street, and as I wouldn't let him cry I would have to stop the car and get him out to cuddle him, it used to take me ages to get anywhere. The car seat was the most expensive one and was all beautiful and velvety but he hated it, so in the end we borrowed a capsual and that worked. He was diganosed with reflux and the angle of the car seat really hurt him. We put him back in the car seat at about 41/2 months and he was fine even falling asleep all the time, then also turned the car seat around at 6 months and haven't looked back since, he can see out the window and our seat reclines back so that him is still laying back but faces forward. We put him in the middle so that he can see out the front window. Also I put his dummy onto a dummy tie and connected the end to the strap on his seat so that when he lost his dummy I could feel for the tie then put his dummy back in without having to pull over. Also at about 6weeks we worked out that Bailey was attached to his muslin and was crying for that because he stop and snuggled into it when we gave it to him, so thats know his cuddley.
I also used to sing songs to him and in hearing my voice that used to help, he loves "5 little ducks" best.
So my best bit of advise is turn his seat around if you haven't all ready done so, use a dummy tie and try a thing his attached too.
Good luck, let me know how you go,
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