Any chance they could be mozzie bites?

Also, my DD had something similar when we moved house - turned out all the disturbed dust reacted with her sensitive skin. If your Dog has been outside, they may have brought some pollen in or dust which might agrivate his skin.

If he hasn't been exposed to anything new, I don't think it will be an allergic reaction (also, they tend to be over the whole body not just one part). But, if you feel at all concerned or worried, feel free to make a Dr appointment and get some reassurance everything is ok.

HTH

MG