Newborn rescue kitten

My friend found a newborn kitten, and brought it to me. Poor little bay was near dead when I got him, cold as ice and covered in mud and rubble. I got him cleaned up, warmed up and fed. Hes now on day 2 and doing very well. **Update. Unfortunately, this little boy caught a nasty infection, I noticed at his noon time feeding that his anus looked a bit raw and red, I put ointment on it and put him down for 2 hours. When I got him up again at 2Pm he was lethargic and wouldn't eat; so I layed down and wat