My Husband 57 Years Old And Healthy Got A Boil

My husband 57 years old and healthy got a boil near anus, it was painful and has gotten smaller with antibiotics warm baths etc. He has had them before. Ive researched and it seems it could be anal fistula. His last colonscopy was 2 years ago. His next one is this September. Im worried. He saw a small amount f blood in on his stool yesterday and is constipated intermittently.