For Almost A Month Now, I've Had This Thing On

For almost a month now, I've had this thing on my leg, between my knee and ankle. At first it was a bump. It didn't bother me much and it was just a little red. Then it would irritate me a bit.
Last Wednesday, I poked at it because the bump had turned a purple-y color. I assumed it was blood so I poked at it with a needle and none of it came out. Yesterday, I took a shower and when I came out, I noticed that blood was coming out of it, so I looked at it. I poked at it until blood stopped coming out. It wasn't that much and it also came out with almost clear, maybe a tad yellow, liquid. Then there was a tiny hole. It's not very big, blood is still coming out, but only a little bit, it hurts a little when I touch it, and the area around it is still purple-y and red.