Sad realities

My 30 year old brain and my 50 year old body appear to at odds with each other. I used to think that people who were so heavy that a short walk was an immense undertaking were embarrassing and so beyond me and the truth is, I am one of those people. I've been trying to run and increase the intensity to my workouts, because mentally, I feel like I can do it. But the first time I tried to d the c25k, my ankles hurt so bad I thought I'd die. When did I become like this? This past week was a good week, I made it to the gym twice and I went for walk/runs outside twice. I ate good mst of the week and tracked everything with my fitbit and lose it. But I Wei myself daily and my numbers all over the place....and not decreasing...what gives? This is what makes this journey so hard. And each time I'm re-losing the weight, it frustrates me more