Hi.
Thanks for your query.
Noted the history about a 40 year old having weak digestion since childhood, now that the simplest foods cause distress, have BM 4-5 times a day - semisolid and whitish yellow in color, gives weakness, has bone-pain - reduced vitality.
The most probable causes of such problems are:
Irritable bowel syndrome.
Intolerance to certain foods and beverages.
I would advise you the following:
Stool tests for three consecutive days.
Tests of blood: CBC, sugar,
thyroid function tests, liver functions and other as indicated.
Ultrasound and
CT scan of the abdomen.
Upper and lower GI
Endoscopy.
If all the tests are normal, this may be taken as IBS.
If the specific reason is found get it treated and you will be fine.
Stop all the foods and beverages that instigate or enhance the problems.