Tough to say whether it's caused by depression or schizophrenia, since apathy can be caused by both. Other than not caring, do you feel depressed/sad/lonely/guilty/hopeless? Is your sleep off? Any changes in appetite? suicidal thoughts? If so, I think it's safe to say you've got some depression going on too. If you're still confused, try looking up the negative symptoms of schizophrenia and the symptoms of depression and seeing if you relate to one more than the other (although keep in mind it could be both).