I have a problem with picking at my gums?

Well I have this obsession with picking at my gums. I am 11 and it has become a habit which I do often. I ucually pick aat them until I cant really pick at them anymore. I still pick at them when they bleed. I usually pick at them for a few days, leave it and then start again. Any advice on what it might be or what I can do to stop it?