How old is your dog? Are you sure you are not seeing the bulbous glands? You can Google that for photos.
Not sure unless maybe it is a hernia.
I have no idea what you mean by "large" but if it is large enough to be obvious to the eye if not looking for it, then it seem large enough to check.
How old is the dog and what breed/mix? What is its general health, and has it been checked by a vet in the last 12 months?
Someone may have some possible related experience, but from the little you have told there's no way to be sure what you are talking about.