My anus itches, and pus is coming out of it and it is painful, what is it and what should i do?

image

It has been one week now. It started with intense itching, and then pain. Then pus started oozing out of my anus. I took a picture and this is what it looks like. I went to the doctor, and we ran some tests but he said that what I have is an infection. Please what kind of infection is this? Has anyone gone through this before, and what can i do about it? Thanks