What could cause my dogs bumps?

I let my dog outside in the backyard for the night and when I let him in, about an hour later, he had these dime sized raised bumps all on his back and hind legs. He was out with his buddy (my female pitbull) and I know they play a little rough and sometimes he gets a single bump where she might have bitten him a little too hard but NEVER this many. I was wondering if it could be bug bites but the fogger company just sprayed our whole neighborhood yesterday. My two other dogs do not have any bumps at all. I know he doesn't have allergies cause I've had him since he was a puppy. I was thinking about giving him bendryl but just don't know what to do.