Black Stool Scared Please advice?

Ive been to doctor 8000 times for stomach pain and all this mumbo jumbo im on prilosec and going in for a colonoscopy on tuesday however my stomach was kinda burning over the weekend from having tummy flu so i took so maalox total relief and the day after that black stool and today black stool, im not sure what to do since i havent had problems with black stool until now how long should i wait to see if my stool returns to normal...thanks!