Lamotrigine

I've been told for years that no medication can really help someone with BPD, yet I finally feel stable on lamotrigine. Tha fuck!? I've suffered for so many years despite all the therapies I've been through when it could have helped me all along? I do suspect I might have both BPD and Bipolar, but the psychiatrist I saw for only an hour told me he didn't think so, but that he could not say for sure in just a single session. Anyone else been through something similar?