did they do a blood panel as my concern is pancreatitis if that painful? Did he get any high fatty foods ? Heartguard i am not that familiar with but does have ivermectin in it is it safe to give to that small size pup? So sorry
here is some info on coccidia
Coccidia (Coccidiosis) in Dogs: A Cause of Diarrhea
more info on diarhea
Causes, Diagnosis and Treatment of Diarrhea in Dogs
pancreatitis
Pancreatitis (Inflammation) in Dogs