I agree it’s best to get a professional diagnosis - but for what it’s worth, I was diagnosed at 17 and I have a similar issue, in that I find it difficult to arrange the thoughts in my head properly so I can deliver a cohesive “thing”, whatever it is I want to talk about. I feel if I had a better (or even photographic) memory a lot of my problem would be solved.
I often doubt my diagnosis, but I haven’t taken a single online autism test that said it was unlikely I had it. I do know the tests are meant as an indicator tool, though - if you get a high score, it’s probably worth going for an assessment.