Once the stomach and bowels increase in size (become big) and remain like that for some time, even if you loose a lot of weight, they will not go back to their original sizes. You could try some exercises which increase abdominal muscle tone. If after a few months, you still think this is an issue for you, consult a general surgeon; maybe surgery be beneficial. But leave this option for the very end.
Congratulations on losing the 90 pounds. The health risk of obesity is more important in the long run than the way your stomach looks.
But as for the stomach, how tall are you? I'm 5'10", and the weight at which my stomach is flat is around 155 lbs. There's a chance you need to slowly and steadily lose a bit more weight, no more than about 1.5 pounds per week.
Abdominal exercises are good for toning the muscles, but they don't do anything for fat around the abdomen. Burning calories and eating fewer calories are the way to lose stomach girth. The abdominal exercises just strengthen and tone the muscles.