Fruits aren't filling because they're pretty much water and simple carbohydrates. You need protein & complex carbohydrates to stabilize your blood sugar over a long period of time, and some fat to feel satisfied. Here are some suggested snacks you could eat every few hours. Since I don't know your size or activity level I can't prescribe quantities (you'll have to figure that out on your own), but each snack/meal should have something (or maybe two or three things) from each category:
Proteins
Eggs, cheese, yogurt, meat (sliced turkey or chicken for sandwiches is a handy option), tuna, whey protein powder (great for smoothies), tofu, nuts/nut butters, fake crab pieces (comes in easy packets for convenience and is great on salads), cottage cheese
Carbs (simple and complex)
Whole-grain crackers, cereals, breads (a good rule of thumb with these is to avoid anything white and/or "smooth." It should be brown and grainy); vegetables, fruits
Fats
Nuts/nut butters, fatty fruits such as avocados or olives, mayonnaise (great with tuna or on sandwiches), salad dressings (oil and vinegar varieties are preferable to creamy varieties)
It's not the number of calories you consume that matters so much as the composition of those calories. If you are active, 3000 calories a day is probably about what you need. But if you're eating it mostly in fruits, your body is missing out on a lot. Check out The Zone diet as a good starting point. If you're hungry, eat!
