I Feel Hungry All The Time And Seem To Just Eat Rubbish Food, Kindly Suggest

i feel hungry all the time and seem to just eat rubbish food but i'm a size 8 and don't put weight on I m a 19 year old girl, i don t really exercise except walking to where i need to go. I m a size 8/10, not really unfit but could be alot better... i feel i eat ok, but again i know i can do better. I don t always eat 3 main meals in the day, some days i can eat 3 meals and still want more food, but instead of having one piece of fruit as a snack i m not satisfied with that. I'd have crisps, chocolate bars and fruit! and i still feel hungry but then other days i could go without eating atall. help!