If it looks irritated, it may be some kind of infection. The bump is what concerns me. Needs a vet to look at it.
If the dog acts unwell, or is bothered by the lump, I would take him to a vet. If not, just keep an eye on it, and mention it at your next vet visit. My dog is always coming up with lumps and bumps, on belly and skin. I always show the vet, and she say's they are nothing to be worried about. Like people, dogs get moles, and cysts, on their skin at times, and usually they take care of themselves. Now, if it grows fast, or seems to bother your dog, take him to the vet right away.