It's so great that you lost that much weight. Unfortunately, losing it so quickly, more than a pound or so a week (1/2 kg roughly) causes this problem. I have a friend who had gastric bypass and lost over 100 lbs over very quickly. She has lots of loose skin and stretch marks. More than I do and I've had two kids.
I think surgery is the only true way if there is a signifcant amount of loose skin. I've read online about spas that offer skin tightening treaments, but those have less dramatic results and are still spendy.
Also consider that you might have children someday and restretch the skin, so you may want to wait until after.
Hi! Don't you want to undergo some slight operations in getting rid of that excess fat. As long as you have a very good doctor to do that, abdominoplasty (or what we call the tummy tuck procedure) can be a very effective tool in tightening the tummy and it tones the muscles. But, it's your choice actually. Just a suggestion from someone here who have tried TT. Good luck!