I have read in my journal about a case where someone with Addison's Disease presented with depression.
This is why it's so important for your Doctor to rule out any physical or organic problems before we can be more certain about the diagnosis of depression or any other mental health disorders.
One of the things I consider screening for is Addison's Disease. It is a very serious condition which is characterized by a deficiency of a body hormone call cortisol. One of the main symptoms for this condition is tiredness. We check for this by ordering a cortisol level . Now this is extremely rare and as you know "rare things happen rarely", so please do not be alarmed or panic. In the last 13years of my practice, I have only seen 2 cases of this, so we do have to put this in perspective.
This article was just to highlight the importance of getting things properly assessed by your Doctor.