Adoi, first time mom memang panic kan! Dark poop like greenish-brown or almost black tu biasa la kalau baby dapat formula mixed with breastmilk, sometimes the iron in formula or how the milk digest boleh buat warna gelap sikit, not a big worry usually. Tapi kalau consistent very dark, ada mucus, or baby seem uncomfortable, better check dengan doctor just to be safe la, sebab baru 3+ months and senang hati je kalau pediatrician tengok.