At 9 weeks of age, there are a few things that we need to be wary of here.
First, on the most minor end of the spectrum, a change in food, environment, giving dewormer and so forth can all cause a GI upset. It can cause both vomiting and diarrhea. However, it sounds like the food change was done before the dewormer was given and the vomiting and diarrhea has continued past just a few days.
On the more concerning end, perhaps even life-threatening, is the risk of viruses like parvo which can very quickly debilitate a puppy. These viruses commonly cause vomiting, diarrhea, refusal to eat, lethargy, blood in the stool, etc.
Because the history on Boomer is so varied, I would recommend that you go ahead and take him to the vet in the morning for a physical exam and to get his veterinary care started, if nothing else. Because you're unaware of when his last fecal exam was performed, this means we cannot be sure that an intestinal parasite or protozoan is not to blame here. Broad spectrum dewormers only cover hookworms and roundworms, they do not rid pets of giardia, coccidia and other intestinal parasites. On top of this, there is no proof of vaccines and even some dogs who are vaccinated will acquire parvo and other viruses. The vomiting and diarrhea can very quickly debilitate a young puppy necessitating hospitalization where home therapy might have sufficed had it been started a few days earlier. Blood in the stool can also indicate a GI bleed, so antibiotics are indicated.
More info here: http://www.peteducation.com/article.cfm?c=2+2102&aid=467
Did my response help to answer all of the questions that you had regarding your companion? If you have other questions, please reply and I’ll help you further.
Once you're satisfied with our dialogue, please take the time to use the star rating system at the top of the page to leave a rating for me. Until this is done, the website will not compensate me for helping you.