Also, don't feed him a lot at once, goldens are prone to bloat, which can kill them. Better to feed smaller meals but more of them during the day.
I adopted a golden that had been almost starved to death...he kept throwing up also. He was probably the runt and always hungry, then when fed chow...ate too much, too fast and threw it up, and it was a downward spiral of him not getting enough food down.
Definitely get your pup to the vets, and monitor any food increase....with goldens they can pack on the weight when given the chance. My dog, HaHa, ended up being 10 pounds over before I realized it...and I once again had to adjust his portion sizes.
Do you have a picture taken from above? are his ribs showing? It's a bit hard to tell in the above pics. Puppies go through funny stages as they grow. They get pudgy then get lanky and so on as they grow. How much and what are you feeding him?
If you are worried, you need to take your pup to the vet to rule out any worms. Also, my relative bought an alaskan malamute puppy and at about 4 months he was all legs and no meat it seemed. (Lankly legs) He is giant size, but normal fur and still is lanky at 6 months and I can see he is slowly filling out a bit.
First rule out any health problems by a vet check. then, if nothing is wrong, find a good kibble. I wouldn't get the brands of dog foods from your grocery store as they are usually the cheap filling brands that are all grain and barely any carnivore type foods. ^_^
I'm aso for having the vet check it when you''re worried.
but 10 kg is ot unreasonable thin for a Golden Retriever. it's a the under lower limit of the weight tabel 've found online at a breeder.
with 3 months it should have 10-12 kg and with 4 months it should have 14-16 kg.
feed several times a day and feed high qualitiy food for puppies. Everything will be okay.