I have this rather large is lump on my back, it looks a bit like a pimple with a little black pinhole in the middle of it but I don't know if it's a pimple or not. I tired to squeeze it but it hurts too much and when I do all that comes out is blood. It's been there for months and hasn't gone down so that's why I don't think it's a pimple. What do I do? Do I go to the doctors? Help!