Hello, Thanks for the query. Before I respond to your question, let me tell you that the causes of headache are many and this can be due to sinusitis, migraine, tension headache, cluster headache, brain tumor/infection, problem in the blood vessels and so on. Further, the presence of associated complaints like vomiting, nausea, any proceeding signs before headache and weakness of legs/hands etc will help us clarify the diagnosis. With the limited information, I feel that you may be having tension headache and/or migraine. Note that these are the diagnoses of exclusion. Mostly you will benefit with rest, relaxation, regular food and sleep habit along with medicines. You will benefit with medicines like valproate, topiramate, amitryptiline etc Mirtazepine will not cause headache. The common side effects are drowsiness, sedation, dizziness etc. Please consult a local neurologist who will guide you through clinical evaluation and management the way i have discussed above I hope this clarifies Best wishes