I was diagnosed with OSDD during a partial hospitalization program. The only way to get a "formal" diagnosis is through a mental health professional, but if you really just want to learn about DID and OSDD and make sense of your dissociative symptoms there are a lot of great resources online. Internal family systems is a good term to look up. Also there are some good facebook groups where you can share your experiences and get feedback. The main thing for me is that my parts are all parts of me stuck at certain developmental stages and they hold different parts of trauma or serve different roles. I have 2 adults, a teen, and 2 distinct child parts. It was kind of a fracture where a piece of me stayed in the trauma and a piece on me continued forward for each part. Kind of hard to explain. But once it was explained to me it made complete sense, I finally began to understand why I had blank spots in my memory, why I would have had conversations with friends or family but have no memory of them, why I could oscillate between being so extremely high functioning to so self destructive. A lot of it made sense, and once I became aware of my parts and started working with them things got a lot better. We almost never have hijacking anymore, and voices and needs are acknowledged.