C'mon you want to be 90 or even 85lbs, that is extremely light!!
But if you want to lose belly fat I recommend fighting fat with fat. I know that may sound scary and you're probably imaging that you may gain weight rather than lose it, but if you follow the Belly Fat Diet that advocates eating MUFAs (monounsaturated fats) at every meal you will lose weight solely from your belly area.
I agree with estranged911 that you should switch to a raw food diet but would add MUFAs which you can find in natural nuts, olives, olive oil, peanut butter,and avocados,
But at 111lbs I doubt you really have any belly fat!!