Heya! Well done on losing the weight. It's often a problem if you lose a lot of weight that your skin doesn't deal with the change well... A change in the style of exercise (toning?) you do could go a way to correct this. However, I think loose skin is something you'll have to live with unless you really want to consider surgery.... personally.... I wouldn't consider that as an option, but i'm not you!
As for the stretch marks, I can relate. I have loads on my legs, bum, hips, boobs. They're not pleasant but there are loads of products about that help to fade them. I suffer from acne so i'm using bio oil at the moment. It's good for scars and stretch marks and for the smallest size bottle it's about £7. Don't be put put off by the size of the bottle when you buy it when you line it up with the price... it goes a really long way. You can find it anywhere from health shops to pharmacies. Your stretch marks will continue to fade and probably get less noticeable and more thin. There isn't much you can do to make them disappear altogether though, mores the pitty. Whilst I can't say that bio oil has had a huge impact on my skin so far, I can say that my skin feels better when I have used it and my stretch marks don't bother me so much anymore. I used to have a phobia of being seen naked but to be honest, my body hang ups have made me more confident and stronger. I'm not sure how it works, but I think you have to learn to accept that there are things that you can't change. I hope there comes a time when this doesn't upset you. Try to concentrate on what you can achieve and look what you have achieved! You've lost 3 stone. Thats a really big achievement.