My son had back surgery on Dec.16 & has developed a large lump just above the incision site. There is no drainage, he has no fever, only increased back pain. He saw his surgeon today who looked at it & prescribed Keflex, which indicates to me that he suspects some type of bacterial infection. He has a follow-up apt. in a week, at which time the surgeon said, if no improvement, he would schedule another MRI, & has not ruled out the possibility of another surgery. What is your take on this, & what else beside infection could be causing the lump?