wow, thats a LOT of weight in a short amount of time. think about us, gaining or losing that amount and then divide us by half cause that is about the size of a dog, so it is even more dramatic for them to gain or lose 10 lbs.
Well he sounds like a veryyyy good weight to me. But do you know who his parents are? If so, then you can judge if he is on the right track or not. If they were very big, then maybe he does need a little more weight.
Just remember, in the first year dogs grow tall and look sort of goofy, it is in the 1st to 2nd year that they fill out. Kate gained about 20lbs just filling out after she turned one.
So if you are giving him satin balls, make sure he is still exercising just as much and I wouldn't put on the weight as quickly as the vet asked you to. Too much weight too quickly can cause damage to their bones, especially since he isnt done growing yet!