I agree with Amy.... Good Advice.... Just do what you feel is right for you and the baby....Maybe have your therapist talk to your doc, it sounds like you really are not ready to go back..... I hope the dr cooperates and actually listens to you, hope ya feel better, Good Luck!
All I can say is do what is right for you and your baby. Your mental health is serious and pregnancy makes even the most sane individuals feel depressed sometimes. There is nothing wrong with feeling the way you do. Your body is going through so much and not to mention the fact that having a child is emotionally demanding in all ways.
If your doctor won't support your wishes, try having your therapist talk directly to your doctor to plead your case. Your doctor might respond better if they talk to another professional. If you doctor STILL won't help out and you really feel like continuing to work would hurt you, either physically or emotionally, I would personally quit the job. I don't know your financial situation to know if that would add more stress but it sounds like the job is hurting you so you need to take care of yourself and your baby. Those should be the priorities until you can get a handle on everything.
Good luck!