The next time these bumps appear on your dog have them examined by your veterinarian. This is the best way of knowing or finding out exactly what is going on. They may be hives or whorls brought on by allergies. They could be ectoparasites like mites or ringworm. Allergies are a possibility as well. You can try Benadryl at a dose of 1 milligram per pound of body weight given 3 times a day. Do not use the Cold and Sinus variety--only plain Benadryl is safe.
They may be cysts or warts?? These can be from clogged oil glands, so you might want to bathe your dog weekly.
Sounds likes "hives" you need to take it to a vet and let them know about it. Some dogs get it when stressed or worried. Some dogs need medication when it happens.