Dogs will eat grass to calm the stomache, some dogs will develop a habit out of it and will not stop eating. There is a member on this board, said her dog is so bad, she needs to be muzzled to go out for potty.
If he is persistent, and vomits frequently, I would ask a vet for an opinion.
My dog likes to think he is a horse, and will eat grass, but not enough to vomit from.
Sounds like an upset tummy to me.. I'd have your vet check him.
Different dogs eat grass for different reasons.. Sofia has eaten it when she is hungry and once when she was really sick. Always check with your vet. he's still a baby and can get dehydrated easily.
All my dogs eat grass, I tend not to worry too much about it as I reason they are self medicating in a natural way. When we have upset tummy's we reach for the Salts but a dog cannot so they go for what works for them and is available.
If it persists then a visit to a vet might be in order.