For the past year, I've noticed a lump on my back, on the left side, underneath the skin has been about the size of a quarter. My skin is smooth, and to the touch it felt like a pimple, able to be moved around. However, over the past several weeks, it is getting less soft to the touch,feels like it's enlarged, and I am experiencing pain when I sit back on a chair, even if it is a soft armchair or couch.