foxy:
it sounds like you are really not in the right subject.
i get what you have when i try to do something that truly does not interest me.
i can't advise you on what to do. i wouldn't know myself.
it's a hard decision to make, time is quite precious (at least i see it this way).
but being happy about what you do is also very important.
one of my tutors said to me that PhD is a way of learning how to do research not about the subject really.
i try to remember that when i am not sure about what i do or what i plan to do, but hey can anyone do something against their needs/dreams? if yes, is it worth it?
if you are really not satisfied then it's better to change it now not when you are half way through.
hope you make the right decision