I'm so sorry that you are feeling so bad. First, know that there are people here who have experienced the same thing and have gotten through! Second, obviously your meds are not working,so you need to talk to your doctor immediately. 4 serious depressive episodes in such a short time, you need to let them know. If you feel that your doctor is not listening, seek a new doctor, not every doctor is for every person.
Then, remember that there are people in your life who love you. They want to help, but they can't help if you don't ask for it.
Even though you are 22 and you have the rest of your life to look forward to, you are not always going to feel the way you feel right now. Things will get better! Find someone to talk to whether it is a preist, friend, therapist or total strangers, like me. Talking things through really helps, that's freud's whole theory. Just talking about things can make them better!
Good luck
mia