Still pregnant, but scared about PPD already.

I'm worried about PPD already. I've struggled with depression and anxiety in the past and I don't want my post partum period to be terrible. If you notice yourself having PPD issues at the beginning, who do you talk to? I never go to the doctor unless it's my OBGYN, so I don't have any other doctors. Would I just go to a primary care doctor or do you tell your OB? Are there preventative measures you can take?