need to push harder

I'm eating the healthiest ever in my whole life. But I'm in the worst shape of my life. Not only am I the heaviest I've ever been, but I'm also just really out of shape. I can't run without hurting my lungs and my heart. Everything takes so much energy. Which I lose very easily. I eat a lot of lettuce! What?! And I hardly ever eat dessert. Whyyyyyy can't I lose weight? I eat right. I exercise. What else am I missing?