What is a yeast infection on the anus like? can you have it just on the anus and not the vaginal area? can it cause sores on the anus if irritated?

It's possible but...: Anal yeast could occur without vaginal, but not very likely. Usually it would cause pretty much the same symptoms as vaginal yeast -- itching, irritation, and redness. Open sores could result, but usually not. Other possibilities include anal herpes if multiple sores that recur from time to time; or anal fissure if only one. See doctor if you have any doubt about it and/or the problem continues.