Depression itself can affect the appetite... Mine is very low since my relapse and I've lost over 35 pounds and some weeks can eat hardly anything at all. Medication can have an effect and I knew someone who lost their sense of smell after a very long period of depression and that in turn killed her sense of taste and therefore her appetite.

Also depression can lead to a lowered immunity which can lead to other problems, for example a sinus infection can impact the appetite. It could be worth getting checked by a doctor to see if there is something else going one.