Kathy I'm so sorry that you're going through this! If there is anything I can do please let me know.
As far as depression goes, I suffered from clinical depression when I was 17 and 18 and my symptoms were pretty severe. I couldn't sleep, I was fantasizing about suicide (even attempted once), I was in a constant state of sadness for about 4 months before I was diagnosed. When I say constant, I mean that I NEVER EVER felt happy, not even for a few minutes at a time. I was lethargic, didn't show emotion, didn't care if anyone around me lived or died. It was pretty bad. I went to the doctor who sent me to a psychologist for review, and then I was prescribed meds in conjunction with intensive therapy. Only you can know truly whether you're depression stems from a chemical imbalance or if its causal. Meds can only treat the imbalance, but if you're not chemically embalanced they can actually induce depression as well, so its pretty tricky. I would suggest that you try to pin point why you are sad, and if you can't, then go talk to a doctor and ask for them to recommend a psychologist. The psychologist can determine whether they believe you need to just talk to someone or if its something more severe.
Since my dpression I have had instances of sadness that have lasted a few months. When I moved to Toronto from Vancouver, both Michael and I had quit our jobs, and made the move and that was stressful. We moved in a down market, there were alot of unknowns and stress, so I was sad most of the time. I cried every day for about 2 months, but because I'd been through chemical depression I was able to distinguish between the two. Sometimes life events can trigger sadness, but if we take control of them we can become happy again.
I don't know if my rant even helped :S **huggs**