Hi.I would have appreciated your detailed history.
Anyways, the history you have given is suggestive of GI problem as you have pale stools, pain in abdomen and back and
constipation. Constipation makes stool darker.
I would think of
Pancreatitis as the first possibility due to the history of pale stools along with back ache.
CT scan of the abdomen would be better once you get to a Doctor as also tests for Blood- CBC, sugar,
amylase and lipase , urine for bile salts and pigments and stool routine and for Stercobilinogen.
Obstructive jaundice has to be investigated for.
Watch for development of Jaundice and distension, vomiting; if you develop any further symptoms , please visit the ER nearby, do not wait to see your Doctor .
Take anti-spasmodic medicines for the time-being .