I'm not sure whether I should tell you this - but my ds has also been very car sick - starting at about 10 months. He would be sick just going to the supermarket! He is now nearly 7 and still gets sick - but not nearly as often.
There are lots of things that you can do to help, but sadly none that will 'cure' the problem. We have tried the wrist bands, medications etc but without much success. The sickness tablets can only be used when they are older and only really for long journeys. We found that it went in stages - sometimes very bad for a few months - sick on every journey - sometimes not so bad for a while.
It gets easier to handle as they get older - but here are a few suggestions.
-Try not to let them eat just before travelling - but say 1/2 an hour before.
-Fresh air helps - keep window open a bit.
-Try and make sure feet are not dangling in mid air - this adds to playground ride feeling.
-If you see signs of distress - try and stop and let them have fresh air - we have pushed a buggy back and forwards along many a layby.
-Have a sick kit in the car - wipes, plastic bags, change of clothes, j cloth and bottle of water for rinsing off car seat.
-Keep car seat covered in old towel - then if he is sick you can discard and seat is slightly protected. When they are old enough keep and empty ice cream tub somewhere they can reach. My ds was often more upset about being covered in vomit than about actually being sick.
-Distraction helps - again hard at 6 months - but singing nursery rhymes - and later story books then personal stereos help.
-Try to time journeys around sleeps.
You have my total sympathy- it is such a pain for you and so distressing for you ds. I hope he grows out of it soon.