Gas & Diarrhea Problem?

For the past month, I have been having gas, bloated and Diarrhea after I gotten over my Bronchitis and Sinusitis, I've been on antibiotics and Codeine during that time. After I felt better is when I started experiencing the giness, bloated and Diarrhea, I go to the bathroom like 2 times or 3 times a day and stools would be loose sometimes watery. I've been taking Pepto for the last month but not every single day maybe 2 or 3 times a week. I've also been eating healthy for the last month and when I eat regular foods like fast food, my stomach starts to get really irritated. I sometimes take Pepto before I go out so I won't have to run to the bathroom. Does anyone have any idea what this could be? Thank you.