New pups often have explosive tum, could be too many treats or a combination of things.
Re: car, FawkesPup used to whine and howl a bit. I think a lot was to do with the fact that as a tiny pup vet= jab, away from mum, stress.
We did short trips with treats somewhere FUN. So for us, the big park, to the market on Saturday to get treats. He then started to realise car = fun stuff is coming, yippee!
Now he travels like a pro.