You know, I just read the most interesting thing today on this subject and they were saying you can't loose weight (that is the weight you may gain from eating normally) until you boost your metabolism back to normal again from either yo-yo dieting, or severly restricting calories.
Here's the deal, what you have to do (and this may sound scary at first), is you need to start eating ALOT more to get up to, say, 2000 calories. BUT you need to be eating healthy stuff like nuts, eggs, chicken, fish, whole wheat breads/pastas, fruits veggies, and low fat dairy products. Just because you're eating more doesn't mean you can fill up on a pint of ice cream for the calories.

Though, don't feel guilty to have treats too.
Ok, so you do that for I think a month or something (grr I can't remember how long) and you WILL gain some weight at first, but this is an important step to getting your metabolism back up. Then, you can gradually cut back to what you feel comfortable eating, but NOT go any lower than 1,200 to lower your metabolism again. You should loose the weight you regained and then stabalize to where you want to be. Just remember don't go too low or you'll just slow it down again. Add some weight training/cardio in to help with your metabolism and also eat smaller meals more often, but listen to your body and stop when you're full, but eat as soon as you're hungry again.
I've tried something similar to this before, and it worked, so give it a shot.