How do I know whether I am lactose intolerance or suffer from indigestion of lactose in milk?

Symptoms of lactose intolerance include:

flatulence (wind)
diarrhoea
bloated stomach
stomach cramps
Irritable Bowel Syndrome
GERD

Symptoms usually develop within a few hours of consuming food or drink that contains lactose.

MANY PEOPLE SUFFER FROM THESE SYMPTOMS ALL THEIR LIFE BUT BECAUSE MILK IS A RESPECTED FOOD IN OUR CULTURE DO NOT THINK THAT MILK IS CAUSING THE PROBLEM. THEY THINK ITS SOMETHING ELSE IN THEIR DIET THAT IS CAUSING THESE PROBLEMS

Most people are just fine consuming milk in childhood. However, the problems usually shows up in the mid-30s as functional gastrointestinal problems like irritable bowel syndrome (IBS) and gastro-esophagal reflux disease (GERD). While IBS is known to affect about 5% Indians, an estimated 8-20% people suffer from GERD.

Among the lactose mal-absorbers, indians show a higher sensitivity to lactose than their european counterparts. For example, the problems that europeans face upon consuming 50gm of lactose, show up in indians upon consuming only ~25 gms, according to a study by  Sanjay Gandhi Post Graduate Institute of Medical Sciences