Pain from a Sac After Lipoma Removal?

I had Lipoma Removal (for a 5 cm lipoma) in the office of a plastic surgeon ten days ago. It was in the groin area, and as you all have written, came back non-cancerous. Two days after, I complained of a burning pain in the area of the lipoma removal. I was told this would go away, but it has gotten worse. The plastic surgeon who operated on me said she did not know what to do, so she sent me to another plastic surgeon who injected the area with a one step above lidocaine medicine(I was told it would last longer than lidocain).I now notice upon standing in and looking at the site that there is a small sac at the bottom of the incision, actually where I am complaining that the pain is coming from. It's about the size of a half dollar. I noticed this because I was told by the dr who operated on me that I should massage the area. Is this normal? What is causing this? When will it go away and what can I do for follow up care?