Please, help me find out what is wrong with my dog? I'm so scared. Please!?

So my dog has white fur and has been randomly forming these yellow circles around his torso and other places around his body. My dog keeps attempting to lick and itch these circles, and they are obviously annoying him. The last time I took him to groom/cut his hair he formed one of these yellowish/orange circles and I ignored it and his hair got longer so I did not really see it through his hair. Now I went to go cut his hair again and he formed four or five of these circles and the groomer said to take him to the vet to check on the circles, although last time we just thought the groomer cut him. These circles may be from a change in food, grooming supplies, fur knots, etc., but I am not sure of which. Before I take him to the vet I want to do some research of what these circles might be. He is like part my our family and I would be so sad if anything bad ever happened to him. Please help!