MY BABY MOUSE WON'T EAT? HELP!?

i have a baby mouse and i just got it... from being abandoned and i need help. it won't drink the milk or the yolk-milk mixture and i tried feeding it through a baby medicine feeder, and a paint brush. it wont open its mouth, it squirms and squeals. i realized its tail is getting scale-like. is he dehydrated? also i realized he has pooped probably 4 times since 10 last night till 3pm today. is that bad? what should i do to keep him alive?