So sorry to hear you have been feeling like this. While it may not be post-partum depression since you haven't had the baby yet, there are still a lot of hormonal changes going on that can have effects similar to what you are experiencing. If it helps, there is a good little article about it here (http:****) and I think it might be encouraging as you are on the home stretch of your pregnancy journey.
I hope this helps a little, and that you get to feeling better quickly. :-)
You don't have postpartum depression until you've had the baby... you're just hormonal and in your third trimester. All totally normal. Every single bit of it.