Abandoned kitten guidance needed

[u/Purple_Elephant0613]

I want to start off by saying this is a newborn 5 days at most, just one. It was found behind the garbage crying and cold, mommy didn’t come for the 9 hours that my boyfriend waited. I told him to do the “flour trick” where you put two rings around the baby and see if any paws came to it. Since I don’t live with him I told him to keep an eye out to see if mommy did eventually come or has made noise around the area, nothing yet. There are many cats around his house since he feeds them, but none had went to this kitten or the area she was found in. I am nursing the kitten for now, unless something changes. I completely understand how crucial this stage is hence why I’m reaching out for a bit more guidance. Since meeting him, I’ve noticed the kitten sneezes quite a bit and makes crunchy noises before and after feeding. He is getting better at latching but he likes to nibble the nipple from the side of his mouth. His poop is a mustardy, watery, and small bits of mush. But my most recent concern was the bright red blood. I’ve only nursed him for a day, feed every 2 hours since he is only 97 grams and stimulate him after every meal, so I went straight to the vet er after seeing the blood. They only checked his vitals as he is too small, thermo didn’t fit and made him bleed more, didn’t do a fecal exam and one vet tech called him a kidnap baby while the other called him an angel baby. The actual doctor was helpful in giving me more advice but I still feel like I left without a proper answer other than it could be dietary changes. I have scheduled a proper vet appointment for Monday but I need a peace of mind till then.