Hi.
Thanks for your query. 
The classical symptoms of alternating loose motions and 
constipation along with other symptoms is more suggestive of :
Cancer of the intestinal tract. 
I would advise you the following tests:
Investigations:
*Routine blood investigations like Complete blood picture, blood sugar, urea, creatinine, liver function tests, 
thyroid function tests.
*Urine -routine and microscopy
*Stool: routine, microscopy, occult blood, culture and sensitivity.
*
Ultrasonography of abdomen,
*
Colonoscopy All these investigations should be within normal limits for one to say you have IBS
If colonoscopy shows cancer, get a biopsy, CT scan of the abdomen and proceed further. 
Treatment:
Get a course of an antibiotic, 
metronidazole, probiotic and see the results , it is possible that you may get a relief. 
If not, go for further tests .