What are some healthy foods that are filling?

Two years ago I tried to gain weight because I was tired of people telling me I was getting too skinny. I was in my weight range and I didn't feel I was too skinny I felt fine but I got tired of almost everyone telling me that. So I tried to gain weight the fastest way I knew how through junk foods. It took me three years to get a noticeable weight gain. At first the weight wouldn't stay I would just be bloated, and now after those three years I gained 15 pounds but my body feels terrible. I know it's my fault for trying to gain weight so fast the wrong way and if I knew it would take me so long to gain the weight I would have worked on muscle weight from the start! Point is I feel tired all the time. I get tired doing minimal exercise, I sleep more than I normally did and I wake up feeling nauseous. I hate it I feel like I threw my health down the drain, and I guess I did. I have a body type that tends to keep the same weight no matter how much I eat, but right now I don't feel healthy. I started going to the gym but I also want to eat more healthy foods like I used to. I love fruit but it's not filling. What are some healthy foods to snack on that will fill me up? I know oatmeal is a good one but I want more options.