autism in children

Hello i am new to the group and have been told by CAHMS that it was a good idea for me to sign up and see if anyone else is experiencing the same things as me. My son is nearly 9 and is awaiting a diagnosis for autistic spectrum disorder. 

I have noticed that when my son has had a good day at school his meltdowns when he comes home is alot worse, he becomes very aggitated and volatile, but when he has had a bad day he will have a few outbursts but will just shut himself away. I cant understand it. I just never know what mood to expect from him because he is so tempermental and negative. Anyone else have this problem ?