Still sounds like this puppy is having a low sugar problem just like humans the sugar level drop during the late day.. I would keep him away from the other dogs and definitely find a new vet to do some blood work.. As a quick fix try the Karo Syrup a...

As I'm re-reading your post it sounds more like the flea treatment is having a bad effect on this puppy a good bath in Dawn liquid detergent generally removes the flea treatments and you might want to check the FDA or the ASPCA web sites to check on ...

I had a Toy Poodle years ago that had a problem similar to this and my vet at the time had me giving him Karo Syrup mixed with some orange juice to give him the sugar...

The shaking and the extreme thirst is very concerning and I agree with the others "GET A NEW VET" and preferably one that remembers their oath "First Do No Harm".. I might also try some baby food and apple sauce dogs love apple sauce.. Many years ago...

I was concerned some more about your dog so I did a search & found this web site http://www.boston-terriers.com/food.htm and in it they refer to the food that you are us...

Stay away from that pond that's for sure !!

Itchy rear generally means the dogs anal glands are bothering them & a visit to the vet to have their anal glands expressed should solve that problem. I would suggest you doing it but it's mess...