My 9 year old Daughter has been passing gas more than an average person on a daily basis since she was 2, and the daily frequency slowly but surely increased since she was 2. It's not just the frequency though, it's the long, loud & horrible smell of them, and also how it sounds like you would find poop in her underwear from it, but you don't, there isn't any there, it just sounds that way. What is the cause of this?