If I tell my doctor I'm depressed, will he call social services?

Depends. If you tell you doctor you're depressed, s/he won't notify social services. If your depression is so severe that you want to hurt yourself or someone else, then the doctor might notify authorities and you will be taken to the er for a complete psych. Eval.
No. Depression itself does not warrant referral to social services unless you have thoughts of suicide or homicide. And also to a psych facility for full evaluation if you have any such thoughts.