Many possibility. Unilateral headache can be migraine, TMJ pain, temporal arteritis and others including a brain tumor. Start with your primary care physician!
Migraine. One sided headaches could be migraines, tension type headaches and what's missed often, but probably one of the most frequent causes of headache is TMJ dysfunction. Simple analgesics like Excedrin may work in case of all of those headaches. Heat may help as well. If you have visual changes, jaw claudication (freezing), muscle aches, this may be sign of a more serious problem requiring attention.
Why do I get a headache on the right side of my head? I'm a 17 year old girl and they mostly happen in school
Possible Migraine. Unilateral headache with pounding is frequently Migraine. Read about this, see if it fits. Primary care doctors are very familiar with this and can be a big help. Stress, poor sleep menstruation and vision problems can all trigger Migraine (among others). Neurologists can also have a role if the headaches don't stop. Get an evaluation and I hope the headaches go away forever.
Depends. If the headache throbs, it is likely a migraine, if it is persistent, it may be from grinding your teeth or even a sinus infection. If this is a long term issue, only a doctor can help you pinpoint the cause.