Hello,
From the symptoms the possibilities of perifolliculitis and acne keloidalis nuchae need to be ruled out. Perifolliculitis is characterised by small, very itchy pustules within the scalp. Acne keloidalis nuchae occurs when hairs on the back of the head and neck grow into the skin, become inflamed, and cause scar tissue. These ingrown hairs usually occur following a short haircut on the back of the head and nape of the neck.
My sincere advice is to get it examined from a dermatologist. It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.