To add from my own experience, I wasn't diagnosed with Aspergers until I was 28. That was two years ago. I'd been in and out of psychiatrists since I was 12 because of having so many problems with social anxiety and depression but none of them ever picked up on it. Two years ago I kind of 'lucked out' I guess as I was referred back to psychiatry by my GP because of other mental health issues and the psychiatrist I saw this time had done a lot of work with autistic people and within the first hour of our session she said she thought that could be the root of a lot of my problems and then referred me to an Autism specialist for diagnosis. Turned out she was right, I officially got diagnosed with Aspergers syndrome, OCD, and DID.

Sometimes, it really does matter who you see. I'd had so many useless psychiatrists who just didn't listen/care and pawned me off with anti depressants which never made any difference.

As others have pointed out, it's sometimes (depending on how arrogant your Doctor is) not a good idea to suggest what you think may be wrong. I had an incident a few years back now (I was 23) where I was pretty sure the pain I was getting was caused by gallstones. I suggested this to one of the GPs at our practice and he actually laughed at me and told me there was "no way a male of my age could have gallstones". After a year of constant pain and being taken in to hospital three times, I eventually convinced someone to do an ultrasound and it turned out I was right! I had a LOT of gallstones and they were completely blocking my bile duct. After that they decided to remove my gallbladder at last and for the first time in a year I could eat without excruciating pain.