So, basically, he appears to have all the problems that we have seen him having. Now the questions are: Which diagnosis is the primary diagnosis? Is one of the diagnoses causing symptoms that are showing up as a different diagnosis? Can we manage one without exacerbating the other?
Ah, this my son. Throw in a language processing disorder and they're the same kid (although the ASD and GAD are not official, but highly suspected by all involved... diagnoses are still pending).
I start with the issues that occur concurrently. For example, ASD and ADHD also cause anxiety, so I try and teach emotional resiliency (breathing, counting to calm down, etc.)
It's hard because all three can cause similar behaviours. I don't think managing one makes the others worse, unless you are treating the ADHD with a stimulant which can cause problems for the ASD and anxiety.
My solution for my DS is to focus on foundations that are relevant to all three (structure, diet, exercise, positive feedback, self esteem building, etc etc - you get the idea) and then I address the behaviours as they occur. I'm also to the point with my DS where I'm giving him opportunities for independence (i.e. making his own snacks, that sort of thing), so that he's learning skills and confidence. His ASD behaviours are the least prevalent... his major Achilles heel is the "off task" ADHD piece. SUCH a giant thorn that one is.
vwmommy how old is your son? What are his biggest issues at this point?