Is it depression? This horrible feeling.

I have been feeling low for a while now. I have not been able to concentrate on work or anything. I have decided to avoid people because even the silliest of the things are affecting me. I have been complaining about this pain near my neck and shoulder region. I thought it was because of the pain I was feeling low. But turns out I have been in this perpetual state of feeling low. Sometimes I just go silent and blank. Won't be able to utter a work even if I really want to talk it out. Expressing things has become an impossible task now. I feel anxious. And I end up smoking. I workout every day and that's the only activity that's been keeping me a little sane. Otherwise all I feel like doing is just sleep. My confidence level has gone down. I feel I don't even know myself anymore. I just want to get rid of this horrible feeling.