This is a normal reaction for a puppy to a wormer. What wormer did the breeder/rescue/previous owner use? when?
Dogs should be wormed at 4, 6, 8 & 10 weeks old then 3 months on from there. When the course is first started you are likely to see some (or a lot!) of worms in the dogs stool, but this is normal and OK, pick it up and clean the area and move on. If the dog hasn't been wormed before they do it every 2 weeks for 8 weeks (ie, if he is 12 weeks then do it at 12wks, 14wks, 16wks, 18wks) then every 3 months from then for a few months then go from there however you wish.
__________________
8.16 Dogs|1.2 Snakes|1.1 Harris Hawks|1.1 Barn Owls|1.1 Giant rabbits|2.10 chickens|100's of insects
Pointer and Vizsla mad. 
Mr.Underdog <3
|