Seroma is one of the most common complications following tummy tuck surgery in a weight-loss patient. A seroma is a collection of fluid that develops underneath the skin flaps.
Drains are normally placed at the time of the surgery to help prevent this, but fluid can still sometimes accumulate after they are removed. Most of the time, small collections of fluid will resolve on their own although may take several weeks or months. If the collection is large or in any way symptomatic, then it may require drainage by your doctor.
I would suggest following up with your surgeon to have him evaluate the problem and determine if drainage is necessary. Once the fluid has been drained or resolved, and swelling has subsided, I expect your abdominal contours will improve.