The commonly used prescribed diet pill that suppresses your appetite is Reductil. I myself have used every diet pill going, but as Irish Mum says, the key is to eat the right foods that fill you up. Most of the time the hungar is in your head, or just cravings. The diet pills will surpress your appetite whilst you are using them, but you cannot stay on them forever, and once you come off them, your appetite will return.
As irish mum suggests, posts what you have been eating, then people can advise you were you are going wrong.