I am on a diet, I have eaten 3 meals today and had 2 healthy snack but I feel shakey, tired and a little off. Is this normal? (on diet for months)

No. They symptoms you describe (shaky, tired, little off) may not have anything to do with your diet. It's best to get checked out by your friendly neighborhood doctor if you've been feeling this way, especially if it's lasting longer than a few weeks. It sounds like you're eating enough, but we all know there are crazy diets out there, so it might be good to run it by your doctor.