GCSEs may not be for you but there are alternatives available, go and speak to the careers counsellor in your school if you have one or speak to Connexions in your local area
http://www.connexions.gov.uk/
If you are suffering from depression, go to your GP and seek medical help
Having read your previous question about leaving home & living with your mate - you're proposing taking on a lot, leaving school, leaving home, taking on your mate's problems - everything is ifs, buts & maybes. It seems exciting & you may feel you're ready to take it on but I'm an adult I would think twice about setting up home with a friend & her child, I have so many questions I want to put to you and so many I could put to your friend but like everyone else, what I have to say is, stay home & stay at school.