Alot of what you describe does sound like borderline personality disorder to me , i have that too. My care coordinator explained to me that our front lobe which deals with emotions doesn't develop fully in people with bpd. So we don't deal with emotions well , can't control them , minor issues seem huge and it feels like the worst day of our life over something that most people can handle so well.
With bpd meds can't help much or so I've been told my the professionals . its down mostly to therapy which it seems you've been getting . there is one thing you could try , hypnotherapy . i had one session several years ago and it dramatically improved my life for over a year . I've just scheduled to get another session of hypnotherapy and I'm really hoping it will help me . I'm not saying you should get it but its just an option to consider . i might of just got really lucky with my hypnotherapist last time , he was amazing , but i live far from there now so ill be seeing someone else . i only hope its even half as affective.
I haven't really had the usual kind of therapy because i also have agoraphobia and its hard to get to appointments .
Any way I'm sorry i probably haven't been very helpful. i wish you the best of luck