Most of the times Headaches are due to Stress, eye strain, sinus blockage or even Migraine. Very rarely it could be due to something significant like a stroke or tumor. Your headache could be due to stress and muscle spasm. As it is radiating down into the neck and shoulders. Take mild anelgesics with Antacid and rest. If the headache is progressively increasing or associated with vomiting or double vision, you need to consult a Neuro Specialist and possibly an MRI.