Oh.... That's a problem I used to suffer from too. You see, depends on the weight you lost. If it happens fast - there's not much you can do. To be honest, exercises won't help, most likely. If you lose kgs gradually and make some special exercises+body cream, gel or oil (honestly don't belive in any of them, since none helped me)) Overall, surgery is the solution, yes I know not safe. But I did it, because I lost too much and my skin was awfull!! Quite expensive and painful solution, maybe this is why I keep exercising and dieting up to these days. I think you should try some tone up or stretch exercises at gym (there are special group trainings) if your budget allows you. Surgery is the last station you would like to stop at.