Will My Exercise Plan Work for Me?

I am 20, 5'4", and about 140. I am not happy with my weight that I've gained from being on a birth control supplement, and a medication for my hypothyroidism. I have been doing between 45 - 2 and a half hours of fast walking on a treadmill on inclines between 6.0 and 8.0. I have also been doing 100 crunches daily. I have noticed my stomach getting smaller, but my weight being unchanged. Could this be from gaining muscle? When I get back to school, I also plan on doing some cycling... will this help my abs any? I have also been doing leg lifts, too... about 50 a day on each leg... I eat healthy... Lots of leafy greens, white meats, fruits, and veggies and drink a lot of water... How long should it take before I see a flatter stomach or any sorts of results?