I would definitely be getting a second opinion, if not a new doctor entirely. I'm a double major in Psychology and Neuroscience, and of what I know, of what I have learned, the "psychological" vs "physical/medical" distinction, when referencing a disorder, is absolute bollocks.
If you feel a certain emotion, it's because your body is producing and saturating its synapses with a certain neurotransmitter. That's how SSRI ADs work. You block serotonin reuptake, so your synapses are more saturated with serotonin, and that is what improves your mood. If there truly was a distinction between the two, no pill would work, because you can't physically affect something that's not physical. It'd be akin to punching the air in order to hurt it, only even less effective.
The only time when it makes sense to discuss the difference between the two is when you're talking about the causes of depression. The physical biology and psychological side of things is a two-way exchange; biology alters psychology, but psychology can also alter biology. That's the entire principle behind neuroplasticity.
If you're talking about causes (and hence, treatment plans) it makes sense to make that distinction. If the cause of your depression is psychological and based on bad habits you may be keeping (e.g. sustained social isolation, negative cognitive styles) well, taking ADs is only going to suppress the symptoms of your depression, because you're persisting in those habits, or those ways of thinking. It's like numbing a broken leg and continuing to walk on the broken leg without putting a cast on it. You might not hurt anymore (which is a huge step in and of itself), but you're not really getting better, either.
If the cause is more medical/biological, then ADs might be all you need to get back on your feet, although generally speaking it's less clear cut than that. I'm sure I don't have to elaborate on how being depressed can disrupt your life and disengage from healthy coping mechanisms (e.g. talking with friends and family).
