thank you for your query.
What you are describing could be one of two things.
first is abdominal obesity
that is , you have put on weight and fat mainly in the abdominal area.
To fix this, you need to lose weight and consider liposuction
or cosmetic surgery.
The other reason could be a hernia
that is, weakening of the scar of the previous surgery, leading to protrusion of stomach contents through it.
For this also, the treatment is a reparative surgery.
Please consult a Surgeon for proper opinion.