Do your parents know that you're seeing a therapist for those other issues?
If they know you see a therapist, you could talk about co-morbids, and how you read something about Asperger's and some of the things struck a chord, and you're concerned that maybe having lots of therapy for OCD and depression and so on, if there's another X factor that isn't dealt with, maybe it's Asperger's, maybe they called it autism or autistic psychopathy or some other label* then maybe the therapy won't work unless it address all your issues and you work through them all?
*Are you male or female? If you were assessed as a child, and they gave you a diagnosis that wasn't Asperger's, then male Aspies have most commonly been misdiagnosed as having schizotypal disorders, and female Aspies have most commonly been misdiagnosed as having borderline personality disorder, and if you're male and were functioning relatively well, then your parents may not have wanted to mention any 'schizo' labels. Be aware though, I'm just guessing here, I've no idea what your symptoms were, or what you might have been diagnosed with, if anything, I just have some general knowledge of psychology and psychiatry as it relates to Asperger's Syndrome, and those kinds of misdiagnoses were relatively common for Aspies, and of course, if your parents (who obviously knew you better, as a whole, than those making a diagnosis) disagreed with a diagnosis and that it was rubbish nonsense then that might have been another reason not to tell you.
They might be scared to tell you whatever label was used, in case it distresses or angers or confuses you, so maybe you also need to reassure them that you just want to get to the bottom of it, not to accuse anyone of making mistakes or to look to lay any blame on anyone over what happened when you were younger, because the past can't be changed, but you still feel as though something is a bit different about you, and you're trying to figure things out and improve your situation and your life for the present and the future, and while you don't want to rake over the past, you're wondering if there might be any clues in your past that might help solve the problems you're experiencing in the present. Or something like that.