If i only eat when i'm really hungry and only drink when i'm really thirsty will i healthily lose weight or should i eat every 3hours?

It depends: If you wait until you are really hungry then you might eat a lot at that time. If you eat smaller amounts more frequently you should be less hungry & thus may eat less. So this depends largely on which method will result in your eating less food. But what you eat is also important. It is best to minimize sugars and starchy foods and emphasize vegetables & protein foods. And don't forget exercise!