when you gain weight after being underweight, it takes about 6 months for it do distribute properly throughout your body, as it all sits at first in your torso, mainly stomach
Have you ever met someone who was say 200 pounds and then lost 30 pounds?
If so, you might not have noticed,and you thought that they didn't look much different. In fact, when they begin to lose even more weight the skin that used to be tight is now loose. They can still pinch quite a bit.
No matter how much you gain or lose, the skin ( without toning ) will remain the same.
My friend lost over 60 pounds. I did not really notice, ( except her face was a bit smaller ) until she showed me her arms. The skin was just hanging there. She needed surgery to cut off the excess skin. The more weight she lost, the more she could pinch.
Does this help put things into perspective for you? Hope so.