that feeling of nothingness does sound like depression based on what little I know of it from friends/partners. have you read allie brosh's blog at all? might raise a smile, if nothing else:
hyperboleandahalf.blogspot.co.uk/2011/10/adventures-in-depression.html
hyperboleandahalf.blogspot.co.uk/2013/05/depression-part-two.html
it was quoted by a lot of mental health charities as being useful, so I hope you think it's helpful to know you're not the only one if you've not seen it before - literally hundreds of thousands of people all over the world have been there, and have got through it.
she says stuff like:
^ ... "And that's the most frustrating thing about depression. It isn't always something you can fight back against with hope. It isn't even something — it's nothing. And you can't combat nothing. You can't fill it up. You can't cover it. It's just there, pulling the meaning out of everything. That being the case, all the hopeful, proactive solutions start to sound completely insane in contrast to the scope of the problem.
It would be like having a bunch of dead fish, but no one around you will acknowledge that the fish are dead. Instead, they offer to help you look for the fish or try to help you figure out why they disappeared. The problem might not even have a solution. But you aren't necessarily looking for solutions. You're maybe just looking for someone to say "sorry about how dead your fish are" or "wow, those are super dead. I still like you, though." ... ^
I'm so sorry you're having to deal with this; it's such a complicated thing.