Getting a full diagnosis can be really difficult, and many people just never get one. Sometime we just have to accept that what's happening is happening, and we just have to accept that. You may not want to wear a diaper every night, but I'm sorry to say you may have to accept you will. It's the same with needing glasses, hearing aids, wheelchairs, and such.
That all said, there are steps you can take to try and help lessen your need for diapers at night. Seeing your doctor was the right first step. Now try looking into kegel exercises. Doing them during the day can help you at night. Try holding your pee a little longer during the day too. Not for too long, but even 10 extra minutes can help your ability to hold overnight too.
Don't dehydrate yourself too much, but you can restrict water intake for an hour or two before bed. Not so much your pee will turn a dark yellow though as that can invite other problems. And don't drink alcohol in the evening (which given your age I assume you're not). The same for anything caffinated like coffee or tea. Lastly, while obvious it needs to be said. Make sure you pee right before going to bed, even if you don't feel like you need to.