How to Confirm a Medical Diagnosis?

Sometimes education + time will help bring it out. Investing into your own research of diagnostic criteria, the physical things happening in your brain (if you dont learn this part you might not be able to tell the difference on very similar symptoms across disorders) as diagnostic criteria doesnt explain WHY just WHAT. Talk more to people with that diagnosis to see what relates and what doesnt. Keeping a journal of day to day and symptoms can help with insight. And keeping in mind that there is a lot of overlap between disorders that arent even in the same bracket but its knowing where the symptoms are coming from that helps dictate treatment. This is a difficult but important thing to go through with diagnosis especially when doctors dont really listen to you. If you find one of those I suggest firing the doctor and finding a new one if its possible to do so. I hope this gives some structure and lets you find some answers.

I just feel like I don't have the right diagnosis. It doesn't add up in my head to have a whole bunch of "smaller" diagnosis when one "bigger" diagnosis makes more sense to me.

Researching what you've been diagnosed is a good start. Another option is getting second opinions. Do you feel you were diagnosed wrong? Or do you feel you need more diagnoses? Sometimes it takes a long time to get diagnosed correctly with multiple diagnoses. Other times they have it right off the bat. There is no sure way without talking about it with professionals. And being honest with them up front.