Four days ago, I found a newborn kitten. Its mother had rejected it, so I took it in myself because I didn’t want the poor thing to die. For the first two days, I fed it powdered milk intended for humans, but it caused bloating and seemed to give the kitten stomach pain, so I stopped.  
Since the evening of the third day, I’ve been feeding it kitten milk replacer. However, after every feeding, when it tries to poop, its stool is yellow, hard, and dry. It struggles a lot and seems to be in pain, crying while trying to defecate.  
The kitten had never had any mother’s milk since birth. Because I couldn’t find a way to relieve its constipation, I found a nursing mother cat. She accepted the kitten and fed it a little, but because the kitten is extremely small, it couldn’t get close enough to nurse properly. It stayed with the mother for one day, but by then it had become very weak and barely moved, so I brought it back home.  
I warmed it up and gave it small amounts of milk, and it became a little more active. But again, after feeding, it tried to poop and passed hard, yellow stool. Sometimes there is even a little blood in the stool. It struggles so much that it cries, and I honestly don’t know what to do. 🥹  
There aren’t any other types of kitten milk replacer available at the pet shops in my area. What can I do?

URGENT: Newborn kitten is severely constipated, crying in pain and has blood in stool — please help!