Insulin doesn't make you fat, but typically when you have diabetes your eating more regularily and all of that. Another thing is has there been a change in your bloodsugars? When the sugars are high, you typically lose wieght easily(but also gain just as fast) quickley, but when your sugars are within range you tend to gain weight and then its harder to lose it. Insulin doesn't make you fat, but it does store fat.
Fat around the stomach can also be an affect from not getting enough sleep/ sleep deprived.