How Can A Bleeding Leg Wound Be Treated?

I have a bleeding wound on my leg it has been bleeding for over three weeks now and doesn't seem to heal, it was a small mark on my leg that I picked at and now it has gotten huge! it has grown skin over but just bubbles out and fills up with blood when it gets knocked it starts bleeding again, and I mean lot of blood comes out like a constant stream it bleeds through my bandages quite quickly