A persistent, one-sided headache at the back of your head could indicate a tension headache, migraine, or nerve irritation. Relying daily on Saridon and Otrivin can actually cause "rebound headaches" and worsen your symptoms. Please stop using Otrivin if you have used it for more than 5 days. For temporary relief, you may try an anti-inflammatory medication like Ibuprofen (400 mg) after food instead of Saridon. However, because your pain is severe and recurring, please consult a doctor for a proper diagnosis and tailored prescription. Avoid further self-medication.