Pain in abdomen &black loose stool.

I've upper abdomen  mild pain just above belly below ribs after eating break fast it occurs1month ago for 2 weeks pain come &go it self after2-3 hours.doctor  gave 10  rentac tablet  for   acidity .pain not comes .but I have indigestion heart burning burping (any thing eat or drink or not to eat) stomach burning (any sour food eaten)now  my problem is I can eat finger millets ,churmuri ,lightly spice dishes I get sudden pain in abdomen I urge to go bathroom 4-5 times loose black  stool with mucus come.2 months back I tested stool culture , blood cbc,abdomen scan it normal.upto till this like stool comes 2times from 15 days.only one day it happens another day normal stool come.what I have problem sir/mam.