I Have Been Having Severe Migraines For Years Daily, I

I have been having severe migraines for years daily, I get very dizzy and have experienced blackouts. I went to the hospital over two years ago where they did a CT and said there was something abnormal, but then did an MRI and turned around and said I was fine. Any recommendation's on why I could be having these severe migraines? I have problems remembering things I was just saying, and not being able to focus at all at work. HELP!!