Please take him to the Vet.When Buster had internal problems it turned out to be Gastroenteritis ( I believe that was the correct term we thought it might be pancreatitus) I don't have the paperwork with me at the moment. He bleed and I found red blood on his poo pad. He could be trying to poop and all that is coming out is blood. Honestly everyone here is just concerned that you baby is so young and so small. I can't tell you how many times I have cried for a dog I have never met but got emotionally involved with reading posts on YT that died from poor or lack of vetting. We know you are trying to do the best for your dog and are caught between a Vet and a hard place. We may not know the answers but we care about you and your pup. You may need to see a specialist. I am in LA and if you are near the Wilshire/Sepulveda this is a great specialty hospital.
Animal Specialty and Emergency CenterASEC, Los Angeles, CA 310-473-1561 | Veterinary Specialty Hospital & 24 Hour Emergency Center if you are near Burbank this is a great Vet
https://www.burbankvetcenter.com/dr-pavlina-burpee-3/
Sending prayers for your baby and you.