4 Month old Bernese vomiting 4 days now :(

SO yesterday morning, Cooper ate this Brat diet (rice and chicken) for the second time and then got sick.  The vet was able to squeeze us in mid-morning.  Before we ended up going to the vet, we stopped by my parent's house and Cooper turned back into his usual normal self, playing non stop with my parent's dog, Adie.  At the vet, he again acted normal.  He had a slight temperature, but nothing to be worried about.  The vet checked him out and decided not to do blood work or Xrays on him, since he acted fine, his checked reflected a healthy puppy, and was still eating and pooping.  The only suggestion she had was to give him half a Pepcid AC tablet with his food twice a day.  Last night he was fine, just slept a little more than usual (typical after a vet visit...he gets a bit stressed there).

Then this morning we got up and fed him half of his normal kibble with a little rice and pepcid (recommend by the vet).  And yet again, he got sick this morning.  20 minutes later, we were outside on poop patrol and he was running around like a nut, playing with us and tossing around sticks.    The vet suggested bringing in a sample of his stool to double check for worms (even though he has already been dewormed and had his stool checked before).  They mentioned before that if things didn't clear up, then he should have blood work done and probably Xrays as well.   

I apologize for ranting on like this, but I feel like I am at a loss on what is wrong with him.  Has anyone else had anything similar like this happen to their dog?       

Today has so far been a good day.  We ended up switching Cooper's food from purena pro plan to an organic lamb and rice food.  He loves it and has been able to keep everything down so far on it.  I went into the vet today with his stool sample and the test results came back negative for worms...they also said that as long as he is still not vomiting, that he can wait until this appointment on thursday. 

Good news...Cooper has been a happy healthy puppy ever since we switched his food over.  I am still not sure if it was the Potty Mouth pills or his prior food, or even both.  He has rapidly starting growing in size again, phew.  Thank you all for answering my questions and support!