headache & abnormal MRI (doc refers to as unusual)

I have been suffering from constant headaches for nearly three months. During this time I have had a decreased appetite and lost nearly 10lbs. I also have had recurring nausea and vomiting. The head pain is primarily located at the back of my head and seems to increase with pressure. In addition, I have several sharp stabbing pains in other areas of my head and feel a great deal of pain and pressure in my ears.
Two weeks ago I had a MRI of my head which came back abnormal. Latter in the day of my MRI I received a call from the radiologist at the hospital informing me I should go to the ER for a spinal tap. In the ER my spinal tap came back normal. However, the doctor's there told me they never saw a MRI like mine before. They were able to tell me the area of the abnormality is in fact where the pain is, the back of my head. The next week I saw a neurologist and she was able to tell me there is no sign of a tumor and no infection. She did say the MRI is "unusual"  but I was not able to get her to tell me what could be going on. She ordered a MRI with contrast and a MRA. I am scheduled to have these tests late this week. In the meantime, I am going crazy wondering what could be going on. Any thoughts? Thank you in advance.
Sincerely,
Carrie