What about dysthymia? I am capable of feeling happy, but tend to experience long periods of dissatisfaction. When I saw a psychiatrist that's what I was diagnosed with, despite the fact that I think I easily fit the criteria of major depression at most times. The psychiatrist thinks I experience episodes of major depression on top of dysthymia.

In my experience, medication is less effective for treating more persistent and lower levels of unhappiness, than it is for some of the more extreme symptoms of major depression. I'm still relying on therapy to help me with that the most, but it is a very slow process.

All in all, your description of how you feel does sound like a normal reaction to challenging situational factors. Not that that makes it easier to cope with, of course!