Why is my puppy sick?

[sullys_mama]

We rescued a dog abt 5 months ago and she ended up being pregnant and she had 7 wonderful puppies and they are 15 weeks old. We have not been able to give all the puppies to good homes yet so we still have 3 plus the one we are keeping. Yesterday 2 of the puppies had attacked the other puppy. We had no clue why but this puppy is the more quiet and sweet one and less rambunctious than the other so maybe we thought he is just the runt and that’s why they became aggressive towards him. He lost an extreme amount of weight within the past 24 hours and you can now see his ribs. He is refusing to eat but he does want the food and tries his best to eat but he just can’t. He seems very weak and has thrown up abt 3 times. I am wondering if it’s because he’s stressed from being around the other dogs or if something else is wrong with him. Please help if you can.!