The loose skin can be rectified by physical exercises like cycling, swimming or working out in gym to make the skin firm and taut and if there are any stretch marks due to gaining and losing weight, then many treatment choices available for stretch marks like over-the-counter creams or lotions, tretinoin cream, laser therapy can be tried.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.