Bumps on the skin can indeed have different causes: tunor, granuloma, abcess, and cyst. Small (1/4") red bumps, pimples, or small crusts are evidence of a skin infection (usualy staph). Skin tags are small (1/4 " - 3/4") benign growths of the skin that are hairless and pedunculated. The masses you are describing sound larger than skin tags or a staph rash, and if these lumps are new, or if your dog is lethargic, then you need to take him back to have the lumps checked with a needle to obtain cells for analysis to make sure the lumps are not cancerous, and to perform bloodwork/thyroid panel to make sure there is not an internal reason for the lethargy. They may be lipomas (fatty tumors) which are benign, but if they are growing then they should be removed and biopsied. Additionally, the comment about your other dog licking them is odd, are the lumps draining fluid? If needed, your veterinarian can refer you to a dermatology or internal medicine specialist if clear cut answers cannot be obtained.
Kimberly Coyner, DVM
Diplomate, American College of Veterinary Dermatology