Suffering from Temporary Blindness

Please if you can help me with a diagnosis of what could be causing my temporary blindness... I started having this medical condition ever since one hot day in 1996 when I was 8 years old I couldn't see but there was no pain and I still could hear and know what was going on, it was just like I was blind. It happened about 7 times within the first 6 months after I had the first experienced this terrible thing. It then went away then came back whilst I was playing sport at the age of 12 and it has not given me a break. I have had MRI scans, CT scans and EEG scans and nothing has shown up. When I am experiencing these awrful symptoms I loose my vision completely as if I were blind (it is like a tv turning off is what I see before it completely goes) It started off identical to the symptoms I was having when I was 8 years old, but as I am getting older these symptoms are getting much worse I now can't stand up when it occurs and I loose my hearing but not completely yet again I still know what is happening every second. THe longest my vision went was about 20 min but when it did come back everything was orange for about 4-5 min then it went green for boput 10min before returning my vision correctly. I am 19 years old now and have been wearing glasses since I was 15 coz now I am near sighted...when these symptoms used to be very far apart as I'm growing up the blindness happens alot more frequently it scars me. If you could help me with any suggestions that it could be or what can cause these terrible turns could you please let me know.