well there are little yellow pumps on it makes me think maybe he got stuck with something outside and maybe its just a sliver of some kind that's gotten infected... but its not red enough... my guess is foreign object... what are the little yellow things??? are they hard or are they like a liquid?? Let us know what the vet pulls up!!!

 

That looks a lot like a small cyst my spitz-type mix had. It's the same size and shape, anyway. I hope you'll let us know what your vet says.