Have you tried any online therapy? Im sure there is a free CBT site. If you are interested I can find you the link. CBT changed my life when I was about 18 years old. It gave me so many skills for my anxiety that I still use today (10 years on). It sounds very much right now that you have been triggered into this state due to the stress of going back to school, if you can cope with the stress of school then your mood may improve. Im not a doctor of course so correct me if I am wrong, but sometimes it takes an outsider to see whats really going on.