My job

I'm dealing with ppd/anxiety I've been stressed not receiving the same earnings. Unfortunately am more stressed now because my job called me to tell me that if I don't return by oct-18 I may be terminated. I had my daughter April 22. My doctor has been giving me extensions not to mention my HR person wouldn't stop asking if my disability is pregnancy related. Can they terminate me? Do I have to disclose what my condition is? I've done some investigation and it looks like my job position is should not be secure but when am released from disability I am able to go back to any open position they might have. I'm in the state of California anyone please help. My company is more the 50 people if that helps disability told me to call labor commission still waiting on a call back.