#1, you have to give it time. It took 9 months to stretch out the baby skin, its going to take more than 1 month for its to revert back. I seem to recall it taking around 6 months to feel like I didn't have stretched looking skin after my baby was born.
#2, don't expect it to ever be completely tight without drastic measure. Skin is elastic, but only to a point. Gaining or losing weight fast (especially if its weight that goes beyond pregnancy weight) causes stretch marks, which is your skin literally breaking and scarring becuase of too much growth too fast. You can't really undo the stretching done by stretch marks. There are creams and potions that can help some, but there really is only 1 permanant solution, as far as I know.
If you're serious about losing weight and getting in shape and you don't want to have loose skin to remind you of what you used to look like (and to make it easier to return to what you used to look like) I would start saving for surgury. Plan to get it when you are done having kids and VERY near your goal weight. It really is, as far as I know, the only permanat solution. Even the people who win "The Biggest Loser" still can have leftover saggy skin that doesn't go away without surgury.
Good luck!