Am i autistic?

Hi, 

I am a 29 year old women and have been looking at the possibility that im autistic for a couple of years now. My niece was recently diagnosed with ADHD and autism and during that time my family and myself noticed a lot of similarities between my niece and how i was at the same age. As we researched autism in girls more the symptoms seems to familiar to me that i was surprised i has never been diagnosed when i was young; i have been diagnosed with OCD and general anxiety disorder and have been in and out of therapy since about 8 years old. 

I have also taken a number of online autism test (unsure how accurate they are)  and they have came up with a high likely hood that i am autistic. I guess i  am just looking for advise on if i should pursue a diagnosis. Although i think i have a lot of the symptoms i am somewhat reluctant to seek this out because i would have thought if i was autistic it would have come up during my years in therapy? In autistic peoples experiences how often are you misdiagnosed or not diagnosed for whatever reasons? 

I know that if i went through the process it would be quite stressful for me, however, after seeing how well my niece is now doing with the proper support and understanding i think it could be a good thing for me.  

Please let me know if anyone has any experience of late diagnosis even after being in therapy and diagnosed with other things before.