I've Always Been Super Energetic And Optimistic All The Time...i

I've always been super energetic and optimistic all the time...i have a great metabolism and I am just natural energetic. For the last six months or so, things have changed. I am tired ALL THE TIME, I get easily irritated and i have zero energy. I was thinking about making a doctors appointment, but I have this feeling that they are going to tell me I'm just depressed and I really do NOT want to go on antidepressants. Is there anything you can think of that's causing this?