I agree...sounds like an ear infection to me. Fold back and ear and see what it looks like in there. The skin should be baby pink (almost white). If it's more of a magenta color or red than that is definitely the problem and you should take him to the vet.
If the skin looks normal then try cleaning the ears out with a q-tip (be careful and gentle) with rubbing alchol on it. Also try gently pulling out some of the fine hair that grows from right inside the ear.
If this started right when he got groomed...maybe the groomer irritated his ears by cleaning or pulling out the hair himself/herself. If that is the case, I would ask the vet to show you how so that you can do it yourself from now on.
If your baby winces or yelps when you try to touch his ears...then take him to the vet right away b/c that is definitely some sort of infection and should be treated right away.
Good luck and I hope your baby feels better soon.