5 mth old puppy has bumps all over?

My 5 m/o puppy has red bumos all over his belly, legs, and a few on the neck. SOme look like pimples, other just red bumps, and a few just white bumps. Does anyone have any ideas??? He has been sleeping alot more than usual and eating less. I have to literally drag him outside to go for a walk, which is very unusual. Can someone help? We went to the vet last week for the eating issues, the bumps are new.