About 2 years ago I burst a pimple on the side of my face. For a while it was fine, then after some months I noticed that it begin to grow into a pimple again. I burst it again and in months it grew larger and larger into a big bump. I went to the dermatologist and he told me it was a cyst. He attempted to drain it with a needle which didn't really work and then injected it with cortizone. After a week or so I managed to squeeze and drain it. It went down and I thought that it was ok, but after about 9 or 10 months it comes back. Initially it feels hard and as it grows it gets softer as if fill with fluid. It excretes solid and liquid substance and a small amt of blood. It has re-swelled at least twice. What causes this and what do I do to get rid of it for good?