Not losing weight

Hello,
I'm Tania and i have been working hard on losing weight. I been on a simple diet of proper food that i can feel good and keep it for the rest of my life. I have to lose the weight because i have a really bad back and that will help me getting better. So many things i can't do since that the musles of my back are not working and i'm taking quite a good amount of pills.

My main problem is that i been doing a proper diet (recomended by the doctor) and doing some walking on my treadmill (has to be fast walking at the moment again because of my back). and i must do at least more than 3000 steps all day but i still haven't manage to lose weight. quite the oposite i been putting weight. Does anyone else have the same problem or it is just me?