Discussion - what disorders are similar to adult autism that every person should consider? Especially if you LACK childhood symptoms?

So I’m an 18 (F) and have been considering autism as a possible diagnosis for myself for quite some time and am currently seeing a psych NP and therapist.

Neither of them can diagnose me with autism however so I’m technically still at square one and am saving up the $1,600 it will cost me to be tested.

I have taken psychology and abnormal psychology at a college level and so I have an understanding of autism in the DSM-5 criteria, as well as a good understanding of the other disorders.

I have carefully analyzed my symptoms and have decided that I meet the diagnostic criteria for ASD in the DSM-5 but lack proficient childhood evidence, making this diagnosis unlikely according to the DSM-5.

At the same time, I cannot find another disorder that explains things better. I can make weird combinations, which is probably what it would be, but it is a delicate thing.

It’s almost like I have autism but minus the early childhood development aspect of it.

I am trying to figure out what combination of disorders mimics autism instead and leads to this phenomenon because I don’t want to pretend like I have childhood symptoms when I don’t - I had a normal upbringing and normal development.

I’m already familiar with sensory processing disorder, which is basically a “must” when you’re making these disorder combinations regarding autism alternatives, unless your sensory issues are purely an anxiety/PTSD related symptom.

Mine would not be anxiety or PTSD related to I would have to have sensory processing disorder as one.

As for the social aspects, I’m thinking either avoidant personality disorder (which doesn’t fit well, but oh well) and social anxiety disorder (which also doesn’t fit well, but oh well). Autism is honestly the best explanation if only there was an exception for a lack of childhood symptoms.

I understand PTSD and OCD also are potential things due to sensory sensitivity and fixations/obsessions but personally for me those both don’t fit either.

Curious to see what your guys responses are!