I'm lucky and don't get carsick, but here are a few tips that I have heard are helpful:
1. Try to sit in the front of the car.
2. Face forward and look at the horizon. Fixing on a stationary point helps some people to feel better.
3. Don't try to read in the car.
4. I agree with cracking open a window, and using acupressure bands, such as Seabands.
Apparently, the problem has to do with your inner ear. Physically, you're stationary in the car, but you're also moving at the same time as the vehicle moves. For some people, their inner ear doesn't cope very well with this. This is why facing forward and avoiding reading is helpful - your inner ear is trying to cope with the movement so it can't tolerate your eyes moving, too, and if you fixate on something stationary, you may be able to "fool" your inner ear into thinking that you're not moving.
When I was a child, my second-youngest brother had a major problem with getting carsick on long trips. Anything more than 2 hours, we needed to carry a bucket for him. There was a particular seat in our old van where he used to sit during longer trips, because it was nearest the door so he could get out if necessary. We used to call it "The Barf Seat" and would all try to avoid being the last one out if it was a short trip, as no one wanted to sit there if my brother didn't have to sit there.
If it's a major problem, you might see if your provider or pharmacist can recommend something to help with the nausea. Just ensure that there aren't any interactions with any other medications you may be taking.