Lose Weight, Flat Stomach and Diet!?

So I want to lose weight, or at least have a flat stomach. I never used to do exersize, and my eating habits weren’t so great. I’ve started power walking/running for 35 minutes everyday, am doing 200 crunches, and some thigh exersizes. Instead of eating chips or chocolatey stuff during lunch (usually would have Lays or greasy foods), I have started to eat yogurt and sometimes fruit. I’ve also stopped drinking Ice Tea and began to only drink water. I continue to have what I used to have for breakfast and dinner, but these foods are generally healthy.

Is this enough to gain a flat stomach in at most 8 weeks?
How long till I start seeing results?
Any other recommendations?
Is this slight change in diet enough?