What is a lump close to your spine?

Ok so i have this lump in my lower back close to my spine, and ive had it for a year and a half now , at first it was the size of a pea , now it is the size of a golf ball maybe bigger. im just a little worried... it gives me pain a lot , sometimes fevers , or no sleep , then about a month ago i had to go to the hospital and i had cellulitis in my back , on the other side of my lump. And now where i had cellulitis another lump is forming. Im just wondering if anyone knows what this could be?