How to get a flat belly?

I'm 18 and completely changed my eating habits and work out schedule since the year has started. I weighed in at 171lbs Jan. 1st now I'm at 140lbs.I am 5'9. I don't drink any soda pop, eat fast food or fattening foods. I drink 8 glasses of water everyday. 3-4 servings of fruits and vegetables, special k cereal. I run 4-5 times a week for 45 mins+. I do every abdominal exercise, and still no six pack. I've even tried supplements like Animal Cutz and Black Lipo 6. What am I doing wrong?