I think it's important to remember there are different types of anti depressants as well. If a ssri doesn't work, a SNRI or a beta blocker may. The placebo effect is well documented but there are often benefits which, when on the correct medication, can occur outside of that because the patient is unaware that effect would occur.
Bpd with PTSD is an unusual diagnosis simply because the two overlap so closely in criteria that the differences usually mark out which one you have. You could try to see a clinical psychologist.
Any professional who refuses to refer you to someone else because it would make them look bad is not a professional you should be working with. It's unethical. You could try to refer back to the CPN and assessment team.