What else should I try?

I will walk every day or I will ride my bike (at least 2-3 miles) 3 times a week, I have even changed my diet. I haven't had a soda in 2 years and all I drink is water. I stay active, mainly because I have a high energy dog and I need to help him let out all his energy. I don't understand why the only place I haven't lost weight is in my stomach. I don't have a big stomach, but I don't have a flat one either. So can anyone give me any advice as to what else I could try? I seem to gain all my weight in the stomach area, is it just my genetics?