Can anyone advise about my son's runny bottom? He's had a cough/cold/ear infection for over a month now (lots of mucus). Has finished a course of Clarithromycin antibiotic at the weekend. For the last 3 days he's been having 1 BM per day but its yellow, bubbly, very, very smelly and he says it stings his bottom, so it must be very acid. He is due to have a barium meal for unexplained stomach aches at the end of the month, but has never had 'the runs' before.