What Does A Lump In Lower Back Indicate?

Hi, I m a 23 year old female with no health issues besides generalized anxiety disorder. I recently came across a firm lump in my lower back above my buttocks and to the left of my lower spine (around the back dimple area). The lump is not visible but can be felt when pressure is applied. I can only feel it when I m sitting/bending over and pressing down on the area. It is completely painless, easily movable and no bigger than the size of a nickle. It seems to be on the muscle. The skin above the lump is no different than normal and I do not feel any different than I usually do. Because of my anxiety I m worried it could be cancerous. What could this be? It hasn t changed in size since I noticed it 2 weeks ago.