Possible PPD but unsure

To start off I'm a mum of 3 (4 year old twins and 6 week old daughter). The twins are from a previous relationship and live with their dad full time. Lately I'm having trouble coping with my 6 week old. At the start things were great but the past few days I'm feeling numb if that makes sense. I'm not happy or sad. I cried the other day for no reason. My daughter sleeps well and only wakes maybe once sometimes twice a night and my partner tends to her so I'm not over tired. I have a history of depression, anxiety and BPD. I'm on anti depressants but dont feel like they are doing much. I just want to enjoy my baby girl but it's hard to enjoy anything right now. I guess what I'm asking is I'm not sure if how I'm feeling is PPD or part of my history. I see mental health at the hospital my daughter was born at plus another mental health nurse and psychologist but it doesn't seem to be helping I dont know what else to do...