Don't worry, you have a common concern. There are many problems leading to abodominal fullness. First is fat, but you seem to be exercising well without any change in your abdomen. The second is diastasis of your abdominal muscles. When you have children the fascia holding your rectus muscles (six pack) together becomes loose and the abdomen has a round appearance despite exercise and weight loss. In this case, you may require a surgery (abdominoplasty or "tummy tuck") to tighten the muscles back together and to excise any extra skin. This is a common operation. The incision can be hidden in your waist line and the surgery can be combined with liposuction to help define your flanks and remove any excess fat.
The best way to tell if you have fat, extra skin, or diastasis of your muscles is to feel your belly.
If you can "pinch and inch," then there is fat which may be improved with liposuction.
If all you feel is loose skin, then it is likely a skin issue requiring abdominoplasty.
If your abdomen remains round despite tightening your muscles (six pack), then you likely have diastasis requiring tightening.
Good luck.
