Oh gosh, I'm so worried about you. I'm praying really hard for you.
I do have some in-put on this though because the same thing happened to my best friend.
She has all of the symptoms of a tumor, some of which include; vision fading in and out, a feeling of pressure behind her eyes, severe headaches, dizziness, bad vision and there are more.
She had a bajillion tests done and was diagnosed with Psuedotumor Cerebri. For some reason, some of which has a lot to do with hormones, her cerebrial fluides are much higher than they should be. The increase in fluid around her brain (also commonly a symptom of a tumor) results in a lot of the other symptoms.
It's most common in women and especially overweight females (you are not, my best friend is and weight loss is one of her "perscriptopns.") Along with a medication they gave her and routine spinal taps.
Here is some more information on it.
http://www.ninds.nih.gov/disorders/p...morcerebri.htm
This is a possibility and a lot better diagnosis than a tumor. I am praying for you, please let us know what you find out.