What is wrong with me?

I have wondered on and off for several months if I have depression but I keep thinking I am just being stupid. I have felt fine and really good for about a month with no negative issues, sadness, excluding myself, well noticed etc, but the last few days I have felt awful, really down, no motivation, want to sleep all the time, I've called in sick to work for days when I'm not really ill I just don't want to be there, easily annoyed/frustrated, sad, don't really want to socialise, no hope. I've had more long term ie several weeks but don't know if these are 'symptoms' easily cold/hard to get warm, tired/drowsy, easy to lose concentration, changes in appetite, really irregular periods. Last time I went to the doctors for something she was so patronising I would feel stupid going back when it might be nothing. I did ha e blood test for diabetes and thyroid about 10weeks ago but came back normal.

Does anyone know anything that can explain this? Please!