It sounds like you are in a tough situation. Honestly I really think you may need to see a doctor about this hypersexuality. Not a mental health professional but an actual medical doctor. Its not normal for everything that happens to brush against your penis to cause an erection. Heck, in your position I would be afraid of public places in the fear that my pants may turn me on. There are medical conditions that cause what you are describing and there may be treatments for it. It happens in both men and women and the biggest complain due to it is the pain that it can cause from constant stimulation. I know that you really don't want to discuss this with your mother. Is there someone else you might be able to ask to schedule and appointment for you?