I did not have that problem before I stopped drinking milk. Normal GI bacteria also ferment the undigested lactose, which exacerbates the symptoms of lactose intolerance.
Symptoms usually occur with in one to two hours of ingesting a food containing lactose.
Lactose intolerance is common, affecting nearly three-quarters of the world's population. Lactose intolerance is most prevalent among blacks, Asians, South Americans, and Native Americans. It's least prevalent among people of Western and Northern Europe an ancestry, particularly the Swedes and Danish. In general, the amount of lactase normally available in our intestinal gut declines as we age, so that we become less and less able to tolerate lactose. Although our bodies cannot naturally produce more lactase, most lactose intolerant people can handle some lactose in their diet without any symptoms.