Fell off the wagon

Hello! I'm new here at MFP, converted from Weight Watchers. I have a pretty good grasp on nutrition, and although I have a sedentary job I am USUALLY (much emphasis) good about building in exercise before and after work. So I've got the basics, and my problem is actually a crisis in faith-I simply cannot believe the weight will go away. I'm 26, 155, and would like to drop about 20 pounds. (Incidentally, I'm SO sick of people telling me "you're not a big girl! you don't need to lose weight!" punches holes alllllll over my resolve. Anybody else have this problem??) No matter how many success stories I read, I just can't seem to apply them to myself! So...I basically keep losing and gaining the same miserable 5 pounds. Any new perspectives out there??? Thanks!!