Thank you for the query.
Diarrhea and constipation
alternately can indicate serious large intestine disease (even a cancer). Especially at your age (over the age of 50, the risk of colon cancer
rises). This is more probable if you have also weight loss, blood in stool
, nausea, bloated abdomen, abdominal pain
Loperamide wont solve your problem.
Other possible reason is chronic bacterial infection.
The first thing which should be done at your case is colonoscopy. Please force your doctor to do this test. Stool culture test should be also done.
Hope this will help.