Thanks for your question Reshma -
It depends a bit on what your surgery involved and when you started noticing the bulge.
Abdominal contour is dependent on:
Abdominal fat (subcutaneous and intrabdominal)
Skin Envelope -
People complaining of "abdominal bulge" after tummy tuck typically do not have issues with too much skin - that points to issues underneath the skin.
Abdominal fat -
This can be an issue in people who may be a little bit over their ideal body weight at the time of abdominoplasty. Ways to fix this include the tried and true diet and exercise or liposuction. Be sure to allow enough time between tummy tuck and liposuction to minimize complications.
Muscle tightness -
Muscles plication (or tightening) is usually a part of abdominoplasty. Either failure of the sutures or some laxity can cause a bulge. If the change in your contour was sudden or if you felt a pop - think about the plication having ruptured.
This can be the most common cause of contour issues post-abdominoplasty. Patients typically have swelling for two reasons. First surgery causes trauma and the body's response to trauma is to bring additional fluid into the area that has been traumatized. In addition, abdominoplasty involves dividing lymphatic channels (very very small conduits that normally pull fluid out of tissue) - until these channels grow back the area will not be able to remove excess fluid.
It is usually the most dependent (lowest) part of the surgery that stays swollen the longest.
Fluid collections -
Seromas (serous fluid collections) or hematomas (collections of old blood) can cause distortions of contour. Normally this will improve on its own but may require drainage.
In your case it may be a failure of the muscle plication. You should be evaluated by your plastic surgeon. Also consider getting a second opinion.
I hope this helps.