Middle of stomach sinking in around belly button after giving birth? (Photo)

This is what we call rectus diastasis. The two vertical rectus muscles were stretched during your pregnancy and did not go back together. A tummy tuck or abdominoplasty is a cosmetic procedure which you may be interested in. Please see a board certified plastic surgeon for consultation. Good Luck!

People who have especially slack skin in their midsection
need more than what liposuction alone can offer. Typical candidates for a full
tummy tuck are women with drooping abdomens after pregnancy, women and men
who've lost a great deal of weight, menopausal women, or older people with
loose skin due to age. In the tummy tuck, the skin from the rib cage down to
the pelvic area is tightened, and the navel is moved up and secured in a new
position. Alternatively, a mini-tummy tuck is especially effective for people
who look pretty good from the navel up. The main difference between the 2
procedures is that the mini-tummy tuck doesn't require moving or reconstructing
the navel and the incision is shorter than the one made in a full tummy tuck.

Pregnancy induced rectus diastasis can cause a significant shape change to the
abdominal wall, even for very slender patients. Because the tissue between the
muscles has been permanently stretched, no amount of exercise will restore the
shape of the abdomen. Rectus diastasis is repaired through the surgical
technique of an abdominoplasty, or tummy tuck. This skin is
lifted near the pubic hair, and elevated to the level of the breast bone. The
muscles are tightened in the midline where the tissue had been stretched by
pregnancy. Permanent stitches are often used. In the most severe cases,
mesh is used to reinforce the central repair area.
If you only want skin correction and don’t want surgery, you
might consider Thermage. Thermage® is a safe, non-invasive, radiofrequency (RF)
cosmetic procedure that’s clinically proven to help smooth, tighten and contour
skin for an overall younger looking appearance. Thermage® uses radiofrequency
technology to heat the deep, collagen rich layers of your skin. The heat helps
tighten existing collagen and stimulate the formation of new collagen, which
reduces sagging, renews contours, and improves the smoothness and texture of
the skin’s surface. Thermage® can treat wrinkled, crepey, sagging or bulging
skin as well as the appearance of cellulite. I suggest you make an appointment
with a board certified plastic surgeon who can discuss your options with you in
detail.