I've been having really sharp pains behind the left side of my head for two weeks. This morning when I woke up, the pressure behind my left eye was excruiating.... What is causing this pain???
I'm sorry that you are in such pain right now. Any head pain that's been going on that long really makes life much more difficult. Have you tried taking anything to relieve this pain, does that help? Have you spoken with your doctor about it?
You mention "sharp pain" - not headache or Migraine. Have you been diagnosed with either Migraine or a headache disorder? One of the most important things is to get an accurate diagnosis which will allow you to get information and treatment. To do this, doctors usually go by the gold standard for diagnosis, the International Headache Society's International Classification of Headache Disorders, 2nd Edition (ICHD-II). When you get a chance, take a look at The Type of Migraine Does Matter.
Sorry for all the questions, but the answers will help determine what direction to point you in. I wish I could tell you what is causing this pain, but I really can't. Only a doctor, who can go over your and your family's medical history, give you a complete neurological exam, and discuss your symptoms will be able to diagnose you. No one can diagnose over the internet, it is not safe.
Ice pick headache is a primary headache with intense, sharp, stabbing pain commonly on one side of the head. I'm not suggesting this is what you have, rather just providing you with information you can discuss with your doctor. Take a look at Ice Pick Headaches - The Basics.
Do let us know how you make out,