It sounds like you aren't eating enough. Remember, healthy things that aren't excessively processed (for the most part) are very low calorie and only temporarily filling because they are mostly water. 2000-2500 calories in grains, fruits and veg is a whole lot more volume than processed foods. Healthy food also tend to be fiber rich, so they move through a whole lot quicker than meat and fatty/greasy foods.
I normally eat around 6 large pieces of fruit (bananas, apples, pears, peaches ect..) in the morning, plus a large glass of juice in addition to my bowl of oatmeal. Same at lunch and dinner, you have to eat a ton of fruits and veg if you're not eating a whole lot of grains or processed foods. I've upped that even more recently, as I went from ova-lacto vegetarian to vegan. Many vegans get malnourished because the amount of food one needs to eat as a healthy vegan is almost comical so you eat "normal" portions and end up only getting around 1000 calories a day (which isn't enough!). That's one of the big reasons I flip flopped around for years over becoming vegan- while possible, it's really difficult if you want to be healthy. I know I'm struggling right now to consume enough calories without dairy, eggs, soy or unhealthy processed junk. I feel like all I do is eat and do dishes lol! It will get easier though as time goes on (it always does as you become used to it). When I switched from a "junk food" vegetarian to a healthy vegetarian diet, I remember feeling like it was almost impossible to eat all the fruits and veg I have no problem getting through now! This is no different. Hope you start eating an appropriate amount of food and feeling more satisfies after meals soon!