Bedgerly,
Please see the following websites: http://www.pseudotumorcerebri.com/, http://www.ihrfoundation.org/, and especially, http://groups.msn.com/pseudotumorcerebri/_homepage.msnw?pgmarket=en-us . It could be this condition (Pseudotumor Cerebri or Intracranial Hypertension - same thing but two names). You must see an ophthomologist to check your eyes and see if they see optic nerve swelling. Also, you may need a spinal tap to check for increased pressure, just like nikki2129 said above. Start with the ophthomologist. (Pseudotumor always has a normal or clear MRI, but is diagnosed by optic nerve swelling or spinal tap.)
Julie
I would suggest a spinal tap to check for increased pressure.