How to loose weight naturally and permanently?

Im 17 this year. I loose 7kg before this and did it with a healthy diet and exercises. But now i gained it back and i dunno what i can do. Im still eating healthily such as no soda, fast foods and desserts. I exercise around 5 hours a week. I can do sit ups for 100x non stop and push ups (boy style) 50x non stop. Is there anyone out there who can teach me how to lose the weight i gained back? Im sick of looking at the mirror and finding myself fat again.