Older dogs often have bumps or it could be a bug bite or irritated skin, but the best way to make sure it's not something to worry about it to check with your vet. I had a dog pass away from stomach cancer a few years ago, he became very lethargic, stopped eating (and he LOVED his food), and started throwing up. No bumps, but this was stomach cancer and all dogs are different. Just keep an eye out for unusual behavior.