Impetigo most commonly attacks children 4-6 years of age. In fact, it is also called the school sores. Are the sores on your head puss filed, like a pimple and surrounded by red skin? Do they form a thick crust after about 5 days that itches? Scratching will spread it also. If so, then it probably is impetigo. It can be treated with an antibiotic cream that will take care of it.
If the sores on your head aren't like this, then you probably do just have psoriasis.