Service dog?

I have severe aspergers, anxiety, depression, and I'm undiagnosed. I can't afford to get diagnosed. But, I've noticed my dog helps me a lot. I wanted to get a service dog to help me when I have asperger meltdowns, because I have them a lot, and they come out of no where. I can't move when I'm having one, and it would be beneficial to have a service dog in public with me if I'm about to have a meltdown and the dog can alert me. Does anyone have any experience with service dogs? I was going to train the dog myself, I'm currently raising up a puppy from birth.

Thank you for any info ❤️