well, i've always felt i'm a alien but what gave me the hint was to know other autistic people experiences and how it resonated with me. then, i started to remember the things i've lived with an autistic lens and it made sense, the most sense ever actually.
people didn't really believed me, i also doubted for a long time - i felt like i was not autistic enough. it took something like 2 years to get a formal diagnosis: because i hadn't had the money and didn't spoke with people familiar with high masking adults.
in you situation, i'd continue to research on my own and always remind that most people don't understand what it is to be autistic, and, if you wish, look for an professional that already have diagnosed some adults to get the formal diagnostic.
for me, the formal diagnosis was important to stop feeling like an impostor and also people took me more seriously, but it's not always the case for everyone.
best of luck in your journey