sarah–at one point, riley was on 45mg prevacid/day. at that dose, we did notice he was more fussy and irritable. we dropped back to 30mg (our previous dose) and added pepcid instead and that did the trick. my ped’s little boy had what she felt was stomach pain from prevacid, and she stopped it.
i’m sure you’ve considered this but i’m just throwing things out: could he be acting in pain from the constipation and not the prevacid? at that age, riley got VERY fussy when constipated. sometimes to the point where he would scream. have you tried adding mylanta to your regiment of meds? that can help with the constipation, too…
good luck!