You state that your virtual colonoscopy
I also take it you have had all the blood work .
Especially Thyroid ,Celiac and also lactose intolerance
It is important to rule these out. If you have no alarm symptoms
such as blood in the stool, anemia, weight loss etc. the symptom
of constipation, bloating, gas and abdominal pain indicates IBS
(Irritable Bowel Syndrome-C). Your doctor prescribed Movicol which
is called an osmotic laxative. It contains Polyethylene glycol
with Sodium bicarbonate
,Sod. Chloride and Potassium chloride
It makes your colon to get more fluid or water to soften up the stool.
It is effective . The dosage initially should make you have diarrhea,
and after that you start slowly tapering the dose down till you have
normal stool. Initially you might experience some bloating which is
part of IBS anyway.
If you changed to lactulose , which is related to lactose, may make
symptoms worse if a person is lactose intolerant.
I hope you are also following a high fiber diet and drink enough
liquids. Cabbage family of vegetables can give more gas. But
if they are steam cooked , it will reduce the gas effect.
I hope this helps you.
I wish you well.