Starting OVer

Anyone else feel like they keep starting over. Well i am starting over again and i know I can do it this time. I got told by my doctor he would like me to be back to 135 by Feb 13 that was in Feb 12. I was 172ish then and i am now 154. Which is great but now i struggle to diet. I got down to 148 and then got happy and ignored what i knew was good. Now i am back on my shakes and eating healthy this is my first complete week. need any advice to stay motivated.