Since your DS recently stopped the meds he was taking, if it were me I would give him a week or two break before starting another medication. My son is on Concerta, and when he went off it for 2 weeks over Christmas, the effects (which in our case are mostly positive, although he is less hungry) didn't seem to totally wear off for a week or so.

Could you stay home with him for a week, and just have a really low-stress time for a while before starting something new? It sounds like he has gone through a lot at school, with the meds and with this recent bad experience at the clinic.