I`m surprised that any vet would recommend forcing food into pups mouth, as this could be very dangerous to say the least, if you do`nt know what you are doing properly.
And do not feed your pup human food like hot dogs.
If your vet thinks your puppy is in good health all round, then the only reason your pup is not eating is because its not hungry or it just hates the food its being fed.
How OLD is this puppy? That would help in answering your question more positively.
There is a lot of info on this website relating to dogs that won`t eat, and it may help you define why your pup,is not eating:>
http://www.2ndchance.info/anorexia.htm
More info sites:>>
https://www.google.co.uk/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=puppy+not+eating+food
ADD; Just a thought.
Have you had the pups mouth checked out for any problems like sore gums and painful teeth, as he will be teething now and might have a sore mouth. Dont offer any hard food. Soak all kibble until its mushy and add some canned meat to it for taste. But do check his teeth and gums just to be on the safe side.