Why am i so depressed all the time?

I am 15 years old and i am always so depressed all the time, i don't find interest in what i used to find interesting, i get annoyed easily, and i always feel horrible. Last year at this same time i was always happy and i was such a bright person and i loved life. Now i just kind of sit around all grumpy all day and when my friends try to hangout with me i usually turn them down. I went and saw psychiatrist and he said i had adhd and gave me medicine that made things worst and i told him i'm depressed and he said the medicine is anti depression, i am currently coming down from the medicine because i hate it. This constant sad-ness started at the front of the school year (October 2010) and hasn't gotten better. I just want to be my happy, hyper, exciting self i used to be.