Hey I just wanted to congratulate you on losing all that weight and getting healthy. It's not any easy feat to accomplish, especially someone as young as you are
I agree with Steve and Mal in saying that happiness comes from within rather than the external. Loose skin is just sometimes part of
weight loss and we just have to accept that. I think the fact that you are still very young and exercise regularly (and are wanting to strengthen your core) are highly in your favor, so just give it some time.
-Sam