Hi Melissa,
Antidepressants assist the neurotransmitters which are the communication gateways of the nervous system, and therefore cannot be diagnosed through bloodwork.
You pose some very searching questions that I think most of us have wrestled with, who have struggled with psychological issues. And there aren't any really clear cut answers, I don't think. Ask 10 different people and you'll likely get 11 different answers. My own view is that in most cases, there are both emotional and physical factors involved in depression. I say that from my own long experience with it, and everyone's situation is different but that's my opinion.
Antidepressants have been necessary for me at various times in my life and made it possible for me to survive and keep moving through my life. But what has kept me thriving is therapy, which has enabled me to understand my emotional issues and gradually change the patterns. I never would have survived without a good therapist, and I've been very lucky to have a few excellent ones over the years.
However there have also been times when my depression was more than my therapy could deal with, and there seemed to be a physical component that could only be helped by antidepressants. When depression was the worst for me, it was like trying to walk on a broken leg. Antidepressants gave me the splint I needed to keep going, but it was therapy that enabled the break to heal over a long period of time (and is still going on). I required both to survive and thrive -- definitely the therapy, and sometimes the drugs along with that.
If you're not in therapy, you might want to consider it. If you're already in therapy, keep going with it.

If you're not happy with your therapist, find someone else. Sometimes it takes a few tries before you find the right person for you, and sometimes you need to find someone else because your old therapist has taken you as far as they're able to.
I don't know if that helps, but there's my 2 cents worth. Good luck and hang in there!
TheOneInFour