Thank you everyone, I gave Yanni some benadryle and he's not itching anymore. Let's see if the redness goes away.

Is it possible that he could have got sick or fleas from a grooming service?

It's certainly possible, but more likely he may have had a bad reaction to the shampoo they used or from being clipped.

What breed is he, what did the groomer do to him exactly? Was it just a wash and dry or is he a breed that needs a lot of brushing or clipping?