Why Do I Have Fluid Building Up Over and Over 3 Weeks After Lipoma Removal? (photo)

I had a lipoma removed from my upper rectus abdominus on March 7, 2012. I have been back to my doctor twice because the area around the cut has become sore and uncomfortable. He has drained it twice with a needle. The first time he got 6cc out and the second he got 3cc out. I feel that this time it's filled back up with more fluid and has gotten harder since. Why does this keep happening and when will it stop?