I can understand some negative sentiment in contexts where it’s used dismissively (e.g. “I’m [self-diagnosed] autistic and I don’t have this issue, so you’re obviously just a bad person”), or if you use it as an excuse to be a shitty person. Although I’d say that a professional diagnosis wouldn’t make any of these scenarios better.

In your case, you’re experiencing problems and you’re trying to solve them. A self diagnosis helps a lot in narrowing down what the causes could be and help you prioritize different potential solutions to try. It makes no sense to handicap yourself and try to fix things like a neurotypical person when you have good reason to believe you’re not.