Hi there,
Sorry to say, but be prepared for a battle :-/ from my experience, and others I have read about, medical professionals are very reluctant to diagnose at this sort of age.
I knew my DD wasn't quite right from about 16/18 months, raised concerned etc and was initially seen by a paed when she was about 3. Got totally fobbed off, because she was compliant in the 10 minute appointment, and basically told it was a parenting issue, and instructed to do a parenting course!
I let it all go for a while, but then had concerns when it came to arranging starting school etc when she was 4. Once in school, and able to access different professionals, we were referred again, sadly getting the same paed again. Slightly better half hour appointment, but basically fobbed off again, and told I was an over anxious mother and to chill out!
Very very unhappy at this point, I complained (jan 2014), April 2014 referred to a child Pyschologist for a second opinion. September 2014 saw said pyschologist. Thorough assessments, meetings and hours and hours speng with us and our DD, low and behold Feb 15 we get a verbal diagnosis of Asperger's and March 15 official confirmation of it. DD was 7 in March!
So as you can see it can take a long time, and it's such a postcode lottery, that you won't really know until you start the ball rolling. All I can say, from my experience, is trust your own instincts and don't be fobbed off. It's not about getting a label, or even a diagnosis in some respects, it's about accessing the right help and support for you all, and that comes with having the assessments and answers. Good luck!