hard lumps under the skin of my lower back

I have had these lumps on either side of my spine right where those lower back dimples are suppose to be. I have had them for several years and they only cause pain occasionally. I use to be a gymnast and they appeared after i quit. I was thinking they were calcium deposits but now i am not to sure after researching more. They are about the size of a quarter and seem kind of like a flying saucer shape. I can move them around a little bit but not a whole lot. they have become more painful in the last few months. I just want to know what i can do to get rid of them and what caused them in the first place. 25 year old female