My Baby Brother Is Sick. His Poop Has Little Black

my baby brother is sick. His poop has little black strings and his vomit is gushing and yellow. I researched the black strings in his poop and all answers said it came from bananas, but this is impossible because he is 4 months and hasn't started eating solid foods. He is very weak and not his usual active self, and doesn't want to drink his bottle. Does this sound familiar?