Hi Rebecca,
My heart goes out to you. Although my story is a little different, I can really relate to how you are feeling. I went back to school in 2000 to study biology and environmental studies and I was so full of hope and excitement (I always wonder where it came from). I made it through my undergraduate - and then crashed. There were so many reasons that I crashed but I went and got a low-paying (customer service) job and got stuck there. Now any kind of low-paying job makes me feel hopeless, hollow and sick to my stomach. It's like I will be stuck there forever - just the feeling of having to do something no part of you wants to do... I have so many interests - art, chemistry, sociology - but I can't seem to get myself to move on any one of them for fear I will lose it again.
But in this case, I commend you for sticking it out. It will lead to better things - and to the area that you really want to be in. However, it sounds like maybe your depression is making it worse. Ugh. I'm so sorry - and know how you feel.
Maybe you've worked out the best way to do it... get by in your classes, focus as much as you can on your writing and the other things you love and be gentle with yourself. Try to get out whenever you can... to open spaces and the places that make you feel a little better.
I know how you feel about the homesick part to. I can't tell you how much I miss Miami right now (my hometown). I keep having this fantasy that I will just buy a ticket and go - and disappear into the mangroves! :P