Brain Fog - Wierd Symptoms (please help!)?

Over the last couple of years, my body has been doing wierd things. Lately I have had only what I can describe as brain fog, decreased mental capacity, always tired, can't focus. Other symptoms I have had are trouble sleeping, bowel changes over the last 2 years, ual impotence, anxiety, panic attacks and fatigue. In the last 6 months it has gotten really bad and now I am having problems staying awake during the day (I get 8-9 hours every night of rest). I was completely healthy up until the last 3 years or so and since then the doctors have been able to find nothing. I have had bloodwork, urine tests, Upper GI, 2 Brain MRI's, and stool tests with nothing found. Doctors say I am fine, but I know I am not. I don't think I am going to die, but I think something is not right with my body. I am just really frustrated as my symptoms cause severe anxiety. I don't know what to do, anything you can contribute would be great.