When I read the DSM, I think I fit a whole bunch of diagnoses. There is a lot of overlap. For me, I want help with the symptoms that are disabling more than a particular diagnosis, so one thing I would wonder is what would happen if you bring up the troubling symptoms that are getting worse and ask for help with those? If you get the help you need then it doesn't really matter what they call your diagnosis.

Another option you might consider is having a full-blown psych assessment done. They are not cheap, but insurance might pay for it. When I did mine, there was several hours of doing assessments, followed by a couple hour long interview with the psychologist. He then did a written report that was 5 or 6 pages long. That might either convince your treatment providers that you do have PPD or reassure you that that particular disorder is not among the issues you need to address.