huge blood blister that won't go away

I have no idea how to begin to treat this thing let alone what caused it. my flanges are the right size, it's on the tip of my nipple, it never touches the flange so I'm really not sure what I'm doing wrong. I've had it for awhile now, but it gets a bit bigger with each pump. It gets smaller in between pumps but right after pumping it's like the size of a blueberry. I know I shouldn't have but I tried to pop it when it first showed up and that deflated it for a bit but now it's back. What do I do? It's so painful! :(