I went from 44kg to 78kg over 2 years.
Oh wow... you went from 3rd place in a chess tournament to karate black-belt. (But seriously what was the medal for?)
Personally, I'm 1,78m (5'10) and weigh around 55kg.
A year ago I served my military time and had 53kg as i started. During that time I got up to 60kg, so I can confirm that exercising really does help (obviously). But when that was over and I went back to being a lazyass, my weight went back to 55kg, my current weight.
But you know what, I dont really care. I may look like a skeleton but I'm quite okay with that. Love your body (tm)