Being overweight has nothing to do with Hidradenitis. Doctors do not know what causes it, or how to treat it. Those websites are so old and outdated that there is no new information to give on it. There are a lot of skinny people with HS...Yes...You can get it without having sex. I got mine when I was 10, and still have it 35 years later. This disease is incurable, but treatable temporarily...with surgery.
Yes, you should tell your Mom, and then see your doctor. Ask him about HS, and he will tell you what he knows. You don't have to tell anyone about your condition so it won't get around anywhere. No, HS does NOT Cause Cancer or I would have been dead years ago.