Left sided headaches can have various causes, including tension headaches, migraines, sinusitis, or even more serious conditions like brain tumors. It is important to consult a healthcare professional for a proper diagnosis and appropriate treatment. They will evaluate your symptoms, medical history, and may order additional tests if necessary. In the meantime, you can try managing the pain with over-the-counter pain relievers, applying heat or cold packs to the affected area, practicing relaxation techniques, and maintaining a healthy lifestyle. However, it is crucial not to ignore persistent or worsening symptoms as they could indicate an underlying health issue that requires prompt attention.