I Was Sitting On My Riding Mower, Turned My Torso

I was sitting on my riding mower, turned my torso left to bend over and pick up something and felt a huge pop bottom left rib cage. A couple of days later, I went to an Urgent Care and took x-rays. Nothing popped out of place or fractured. However, still hurts and I feel something under the skin move (between skin and rib, puffy pouch about 2 ribs from the bottom rib). They could not tell me what it really was. Any idea?