worried about my new puppys health

Question
i acquired a male boxer puppy about 5 days ago.
he is all white but seems to hear fine and such.
he is 8 weeks old and as soon as i got him home i got concerned with how he was acting.
seemed very tiny,barely eating/drinking,sleeping for hours and only awake for 20 minutes between, and his back end seems weak and clumsy.
then i noticed worms in his stool and and he soon started throwing worms up too, so i immediately contacted the vet and got him in.
the vet told me he seems pretty alert to him but he is very underweight as his hip bones and spine show easily, he is 4lbs 8oz.
it was found he has sever round worms and was given a dewormer.
also the vet found a heart murmur as well, which after all my research on the breed i never came across anything that said boxers are prone to them which im in shock over the fact i never read it...but im hopeing it will correct itself.
the vet also said he isn't concerned with how much he is sleeping for now since he is still so young.

i just wanted to double check with you on how concerned i should be since the vet seemed to think he is going to be fine soon, he is so frail to me.

just by reading a little bit i think im feeding him very wrong, ive always just fed my dogs/puppies 2 times a day once around 9am and then again around 5pm, and according to what im reading it should be every few hours am i right? the only thing is when im feeding him he is only eating maybe the equivalent of 2 table spoons if not less and leaves the food very easily and quickly.
does not drink much either. i got him puppy kibble and some moist puppy food too and mix a tiny bit of both together. the vet also slid a can of their dog food infront of him to see if he ate and at that moment he did alot which shocked me, they sent it home with me to continue with but now he is blearily eating it too and im not sure why. i noticed he would go over to our other dogs dish after she is done and he licks the bits off the edge like he really likes it so i decided to put a small amount down for him and he turned his nose up only difference i see was it was chicken and i was feeding the adult beef flavor could that be it, and is adult food bad for puppies? sorry i feel like im just rambling, i just feel so bad for the little guy and want him to feel a bit better and get a bit more weight on him.
also one last question the vet gave him the dewormer and about 1-2 hours later he threw up again alot of worms and that dog food they gave him, did the pill get into his system ok or did it go to waste when he threw up? i was told id see alot of worms coming out with how bad he was but i don't think he has had a bowel movement today at all that ive seen.
thank you for your time with any help for this little guy.

Answer
De-worming him is a three time ordeal-- dosage every three weeks. I do not know why a vet would give a pi8ll. Get a new vet. You should have been prescribed a small bottle of yellow liquid called Strongid-T de-wormer. It smells like bananas. Most vets will give you a needleless syringe to draw out 1/2 cc to squirt in his mouth orally. It is a broad-spectrum de-wormer for parasites of all kinds.

Also, heart murmurs are common in Boxers.  Most puppies out grow heart murmurs, but some do not. This must be checked periodically to be sure-- up to 1 year old.

You feed a little puppy every 2-3 hours- just like a newborn baby Not tablespoons, but their paw size amount of food- like we measure our fist for stomach size. I would feed him more than that for now.

Get educated. Learn about the Boxer breed. Learn about caring for newborn puppies and young puppies.

Join boxerworld.com and boxerforums.com and read the posts by other Boxer owners and learn. Their are sections to choose from and you can post anything and get answers.

Get a new vet. Learn. Use the guideline of a newborn human baby-- because he is much like that at this point. Puppy proof everything- keep him in a large crate overnight and when he cannot be watched and supervised every minute. He will pee and poop every 30 minutes to an hour for months. His bladder can only be held once he is 4 months old and not for long.