What Causes Foul Smelling Stools?

I have UC, Ibs and gluten sensivity. Recent bouts of loose stools which are sour smelling. I ve been having flare on and off since September 2013. Not getting better with the usual salofalk enemas and mezavant. There is no blood in my stool and my gastroenterologist has done my blood work and tested my stool.For the past 12 mornings I have been taking 1/2 teaspoon bicarb soda in a glass full of water on an empty stomach 1/2 prior to eating or drinking. My stools are now formed and only passing 1 or 2 motions in the morning, but I still have a sour odour in my stool. Could it be the milk and yoghurt I eating? Is it harmful to continue using the bicarbonate of soda? Thanks