You're revealed the problem already. :) You said it yourself:
" the more I tell myself I'm on a diet, the more I want to eat."
THEN STOP BEING ON A DIET!
Sparkpeople has found that the more people play with being on a diet, the less likely they are to succeed. Instead of going on a diet, start making healthy lifestyle changes for LIFE. This isn't some short-term quick-fix. You're not going to eat healthy for a while, and then go back to the way you got fat, right? Well, you don't want to, anyway.
Here's an article that really helped me change my perspective.
Stop Dieting, and start LIVING! www.sparkpeople.com/resource/motivation_ar
Ditch the diet, because diets don't work. Start making small changes to change your habits and lifestyle, and you'll find that you don't have to deny yourself anything that isn't "diet" food because it's all okay in moderation!