Hi Robyn-
The breeder should have recommended the pup to stay on the current food for 3-4 weeks before switching to another brand. While we do our best to make them feel comfortable and welcome in the home, they can experience stress from a new change of environment which can lead to GI upset as you are experiencing.
Once you have had the pup for 3-4 weeks you can begin a slow transition over 7-10 days to the new food. 75% old food 25% new food for the first few days then 50-50 for the next few days, then 75 new food, 25 old food until the pup is on 100% new food. A 50-50 transition 4 days having the pup is way too much too fast for a young stomach!
Hope this helps
