Another piece of the jigsaw puzzle - according to our kids' pediatrician/specialist in ADHD etc, Obsessive Compulsive Disorder (OCD) can be eased, by easing a person's anxiety. So the corollary should be - if anxiety is ramped up, then any latent Obsessive Compulsive Disorder (OCD) tendencies are likely to emerge.
If your child has a diagnosis of ADHD/ADD and increasing anxiety is showing more symptoms emerging that suggest at more, then chances are those symptoms were going to show up anyway. Also chances are, it's always been more than ADHD. It just takes longer sometimes to fine-tune the diagnosis.
I just did a quick check on Google and found some interesting info. Although this site I've grabbed here mentions something about getting kids off ritalin, please be aware that I do not agree with this necessarily.
Anyway, here it is -
http://www.retrainthebrain.com/autism.html
See if you can find any commonality in your son. I was interested to note that they said something about some autism symptoms showing up later. Yes, that can be the case; but you might be also able to look back and see the early signs, they just weren't perhaps obvious enough.
I'd be considering two possibilities - the medications as cause of increased anxiety; and possibly an underlying Pervasive Developmental Disorder (PDD) now becoming more apparent.
Definitely worth looking into.
Marg