Thanks so much for the replies! It's really helpful to know that other people are going through similar experiences. I know the PhD is meant to be a challenge, and I didn't go into it thinking it was easy, but I just feel like I'm constantly hitting a brick wall. It's so helpful to be able to share the experience with people who are also doing PhDs - other people tend to look in from outside and can't really know what it's like. I think you're both right though - quitting isn't really an option now, I guess. That would just make me feel like a complete failure. So I guess there's no way to go but onwards... :S

Hey everyone,
I'm just looking for a bit of moral support... I'm in the 4th year of my PhD at the moment and am in the middle of writing up, and am finding it really hard to convince myself that I'll ever get there. There just seems to be no light at the end of the tunnel.
I was meant to submit last Christmas in order to start a year long post-doc, but the writing always takes me much longer than I think, so I've still not handed it in, even though I'm currently trying to start a new project.
I have two supervisors for the PhD - one is of the opinion that I should just tie up the ends of what I've written now and submit as soon as possible, whereas the other thinks that I should wait and try to perfect the dissertation as much as possible. So at the moment I don't really know what I should be doing. It's becoming harder and harder to convince myself that I will ever get to the end of this dissertation! Maybe I should just quit...
The stress of it all seems to be wrecking my health - I've had bouts of depression since the second year of my PhD and also really regular migraines, which are increasing in frequency again. I'm just not sure how much more of this I can cope with.
Sorry to rant on - I just really need to know that I'm not on my own with this. Surely some other people here have had similar experiences... I'd be really grateful to hear from you.