My little girl was like this. She was a very sicky baby, but the car seat seemed to be the worst, I’m guessing it must have been the position. But she was bad everywhere else too, the only thing I found that helped was using carobel in her bottles to thicken up the milk and did this on every bottle and basically removed the problem
@Katie my LB is breastfed so can’t add anything to milk 😭
How old is he? What car seat do you have? Are you using Isofix or is it belted in? Have you tried in any other cars / car seats?