Hi, If he becomes lethargic or you notice blood in the stool or vomit, he needs to see his vet promptly. As this is a sign of serious illness including a blockage among other things. This sounds like a case of upset stomach, likely from the wormer's and the parasites themselves. You can self treat this at home unless any of the above symptoms start presenting.I would start him on a bland diet of boiled chicken and rice to help settle his stomach.(1 part skinless chicken Breast to 3 parts white rice) If he refuses to eat it mash it up and apply small amounts along the jaw line to force him to eat.
I am concerned with him becoming dehydrated as this is quite serious with dogs. I recommend giving him unflavored pedilayte to replace the electrolytes. If he refuses this as well you can use a small syringe to force fluids into him.