Well I've only started today but my tum is gurgling away-bound to with all the water I think. And I've got quite a bit to drink. I'm passing water alot but nothing else! It makes sense that you'd go more with drinking it I think as when my son was constipated the doctor said I had to get him to drink more. It worked!!
Your body may not be used to the concentrated vitamins and minerals in the packs, or it may be the lactose.
I would split your packs, make them with a bit extra water and if you have them switch to lactose free flavours and see if that helps. Get in touch with your CDC if it continues.