What Does Bruised, Raised Spot On Lower Back Mean?

I know you hear this a lot but, its been 2years now and i have this bruised spot on my lower back, the spot is located in the middle of the spine and spread it to the left. At first it was a size of an egg. Now, its like a size of a sunny side egg. I did went to see family doctor but was referred to dermatologist. She did an biopsy, but negative report came back and it was unknown. Please help. The spot got thinner from the last time.