What kind of cereal are you eating? Even cereals that look healthy at first glance can be deceptive. Make sure you're really looking at that nutrition label. You want to make sure you're actually getting something out of it. And, what kind of sandwich? What kind of bread? What's in it? Are you eating whole grain breads or white bread? Loading it up with mayo and extra cheese or veggies and maybe lean proteins? And do you have dressing on that salad?
Have you talked with your dr about your weight goals? If you really have stuck to the diets you mentioned with no luck, you might want to talk with your dr to make sure its not something else preventing you from losing weight.