Suggest Treatment For Sagging Skin

hi doctor, i reduced few kgs of weight recently. i was on thyroid medication (stopped now) and was walking a hour per day. As a result skin is sagging and looks flabby tummy, what exercise do you suggest for me ?

I am 33 years old, had 2 c-sections. The last one in dec 2007. I am 73 kgs, 5 ft 3 inches.