We just adopted a 7 week old puppy from the animal shelter. When we got the dog we had to initial that they didn't do a parvo test on the dog since they didn't have any. When we brought him home he was active and playing and eating great. My husband bought wormer and thought that the dosage was one packet and failed to realize it until the 3 day that it was actually too much. The puppy was suppose to have one gram of dewormer and he gave him 2 grams for 2 days. He acted horrible on Friday of last week and so we started giving him pedalite through a syringe and we finally switched over to chicken broth. On Saturday he ate a lot of broth and saltine crackers on his own but slept a lot. On Sunday he ate more soup, crackers, noodles and even part of a peanut butter and jelly sandwich and some dog food. Now he hasn't ate or drank on his own anymore. So we have been doing the syringe. Has anyone ever accidentally overdosed their dog and had the same problem? He has vomited up the liquid and had diahrrea that was just liquid a few times today.

Dewormers are pretty safe, not sure what type you used though, still unlikely that you overdosed him.
So, 7 weeks old, adopted from a shelter situation, most likely only one vaccine (if that)
Vomiting and diarrhea.
His best bet is a visit to the veterinarian, sick pups can take a downward swing pretty quickly.
I would take him in and the sooner the better.