
Firstly I would have a word with his/her breeder. As he is only 8 weeks, I would think you have only had him a few days, this can upset tummies.
Are you feeding him on the same as the breeder, if not this could upset him. Personally I would just feed him chicken and rice for a couple of days and see if it settles down.
If he is no better after a couple of days take him back to the vets.
Hope this helps
Sandra