I was diagnosed when I was roughly 30. I had PTSD and Trichotillomania and Generalized Anxiety Disorder for the longest time. They had that nailed down. They had me misdiagnosed with Bi-Polar when I was 16. When I was 19 they said no way I had bi polar but I had the other stuff.
Sometimes it feels like I am losing my mind. If my mind isn't racing a million miles an hour, I get jumpy and anxious over the smallest things or I end up feeling like people who love me don't. Always waiting for that ball to drop.
Best advice I can give you is to take time to learn yourself. Learn when your mind is more or less messing with you. It has helped me a lot. Including with relationships with family and friends or within your love life. Learn to recognize when you are over thinking something more or less. Is easy to jump to conclusions but honestly that usually makes things so much worse. You gotta learn more or less to talk yourself down on things. Realizing when it is your BPD acting up and when you are actually being rational. Learning to separate them can be hard. For me the harder part has been learning to control my out of control emotions and to get my mind to stop racing. I am slowly managing to get a grip on it despite the fact of not seeing anyone over it or being on any medication. Every med they have put me on has not had very goo effects on me so medications are typically a no no. I had a friend recommend Kratom to me to try to help me with getting my anxiety and emotions in control so far so good with it actually. My mind isn't racing anymore and I just feel at peace. And it has helped greatly with the constant pain I have from Fibro. But like medications it can be addictive and you build up tolerance to it. So it isn't for everyone.
This is something that is just going to take time. Try to pay attention to yourself is the best advice I can give. Think before reacting and just go a day at a time.