I know it doesn't seem so at the moment, but you are one of the fortunate ones if you actually do get a dx of PDA... there is still ongoing debate around the condition! Meaning it is extremely difficult to get a dx ithout paying privately.
I know there is also a lots of negatives out there regarding PDA... but try to remain positive that a dx is a positve step nearer to getting your ds the help he will definatley need.
My ds (4.4) has a dx of ASD since he was 3.6, but we know (parents and those working with him) he "fits", PDA a lot of the time also..It was actually a specialist teacher that first raised the subject with me, due to his extreme demand avioidance and very challenging behaviour. Me... well I'm still on the fence, a part of me still thinks the demand avoidance is just part of his ASD. Anyway I digress!
My take for what's it worth is that the label is important, yes, but what's more important is finding the right strategies that work with your child, both at home and school. So whilst I accept tht he fits Autism too, his school are open to working with him and finding teaching methods that fit him. I appreciate that it's not the case at all schools.
If you haven't already found the main support board it's here,
ccgi.pdacontact.org.uk/forum/index.php
Also this is definately worth a read,
www.amazon.co.uk/Understanding-Pathological-Avoidance-Syndrome-Children/dp/1849050740