Write everything you can in your head down. Then revisit with as clear of a head as you can and look for the unhealthy thoughts and behaviors. Those will help you identify the issues and work with them to solve them

I’d examine areas of your life and see where you struggle most and then look for symptoms and issues to focus on. It took a while for me to get diagnosed with certain things so in the meantime I did my research on coping skills related to my specific symptoms as well as the disorders I thought I had overall. If there’s any symptoms you want specific advice on I’d be happy to try and offer some. I’m autistic and have ADHD, anxiety, and CPTSD (which ik isn’t the same as BPD but there’s some overlap lol)