What Causes Pus Filled Pimples On Scalp With Bad Odor And Itching?

I am having Puss pimples on my head scalp.i am having this problem since past 3-4 years.its having a bad smell and itching.when I take head bath pimples will eruct and blood and pus will come.my hair is falling and becoming very thin.please give sugessions for my problem .Thanks in advance.