This is just my opinion here.
You said earlier that you're not "depressed" per say. And I find myself feeling very uncomfortable with the feelings that you say you're having and the reason that is is because there was always this nagging feeling I had in the throws of my depression, something missing, no real reason to be feeling that certain way. I know some people have said its normal to be down but if you have nothing to be down about I think its a problem. I don't think the sadness is healthy if you have nothing to be particularly sad about. That was always a problem for me.... felt sad and incomplete despite everything around me being "fine."
I'm actually glad your doctor is concerned about this because I know you will keep brushing it off trying to make it OK. I care for you a lot Matty (BIG HUGS)