I’m in a very similar situation, diagnosed at 33. For a long while, I was constantly asking myself “Did I do that because I’m autistic?” every time I noticed anything about myself, whether it was odd or normal, common or rare. In most cases it was easy to think of equally convincing scenarios supporting each answer, which was confusing. At times I found myself thinking everything I did was the result of autism, at others I found myself doubting my diagnosis was correct.
The more severe a case of autism is, the more likely the symptoms will be noticed early. If you make it into adulthood before being diagnosed, you’re pretty much guaranteed to be on the high-functioning end of the spectrum, with symptoms less obvious and more subtle than many of the examples you read about. Much of what’s written about autism is known from the study of children, who generally haven’t learned how to compensate, which makes their symptoms easier to observe, and the examples most frequently reported are usually the most severe or bizarre ones. I’ve seen very little written about typical symptoms in adults, or about typical coping strategies and common methods to compensate for symptoms, possibly because there are a very large variety of ways which work well enough.
So it helps a lot if you can identify the most fundamental symptoms of autism in yourself, the ones that aren’t side-effects, coping strategies, coping strategies for the side-effects, coping strategies for the side effects of the coping strategies, etc. Also, it helps to read up on what’s normal, since that isn’t always obvious. (Not just because you have autism, although that too. Even normal people often don’t appreciate how diverse “normal” people are, often assuming most people are more similar to themselves than they really are. This is a bias you’re just as likely to be affected by - yes you, reader.) A lot of the time you’ll find yourself questioning a facet of yourself which later turns out to be within the normal range of variation and not related to autism at all.
In my case, I eventually settled on intense sensory experiences being fundamental symptoms, and that worked well enough to explain the other symptoms I have as side-effects, coping strategies, or unrelated, and let me stop questioning whether every single facet of my personality was related to autism. I’m not, however, convinced my model corresponds to reality. It might be a clever but ultimately incorrect theory which explains most but not all of the facts. I may have inverted the direction of a chain of causation somewhere. Even if I’m correct about myself, there’s a good chance many people diagnosed with autism have similar surface symptoms with fundamentally different causes. Certainly there are a wide variety of proposed causes in the literature, many of which appear to explain symptoms equally well while completely contradicting each other. So, as much as possible, keep in mind facts grounded in reality. Theory about autism hasn’t gelled yet, and will lead you astray. (Which necessarily includes my theory, even though it pains me to admit that.)
That said, the initial surge of questioning everything about yourself does slow down as you gradually finish examining most of your own personality traits and behaviours. A decade after I was diagnosed, I still occasionally notice something unusual about myself and find myself curious about how (or whether) it might relate to autism, but I’m no longer constantly re-evaluating everything about myself.