burning sensation in upper middle back with indentation

[Desilyn79]

This evening i kept feeling a small pain, like a burning sensation or a poke on my upper back, and thought maybe my tag was sticking into me. It continued to become more frequent so i tried feeling my back for a possible bug bite, and there’s an actual DENT in my skin, near my spine. it’s small, like the size of a pea... my partner looked at it and said it’s like a dark, almost bruised looking color. it’s so weird! the pain is now a burning pain for sure and becoming more frequent, almost once a minute. Any idea what on earth would make a sudden dent in your back with pain??! thanks!!