One insane symptoms and conditions

i started taking seroquel about 2 years ago, and with being steadily increased in the dosage i have gaine 100 pounds, and i cannot lose anything. I have tried every diet out there, besides surgery. I am afraid to go off them because i have insomnia and deppression, and anxiety soo bad that i can never sleep. and now in reading other persons' effects i am starting to wonder if all my other problems are an affect of this medicine. I take 800 mg. a night just so i can sleep 7-8 hours. How crazy is that??? i am so afraid...