Thanks for query,
As you had impacted colon,itching of hands and all tests are normal.
Have you gone for stool rest?
It is possible that you might have worm infestation causing itching and constipation
Go for stool test
for ova and cyst and afterwards go for antihelminthiasis treatment.
I think you might have ruled out diabetes
Search for some allergen causing itching.
as and when required.
Ok and bye.