Could be pyroderma (a type of moist skin infection) Does your bulldog eat out of a phis plastic bowl? Plastic bowls tend to retain bacteria and can cause a skin infection (which will require an antibiotic for the skin infection from your vet and changing his bowl to a stainless steel one) Good luck!
Unfortunately dogs can get acne much like humans do. Bolting food is a common factor, especially if the pimples are on his face. Your vet should be able to give you a topical to put on his face to help, in extreme cases they may also prescribe an antibiotic to clear it up.
Ingrown hair is a possibility.
