Thanks for posting your query at DoctorSpring.com
I am Dr.R.K and I am pleased to assist you.
I read your post about constipation and about taking movicol.
You need not up the dose on the second day itself.
You can take the same dose for one more day.
On day three compare your stool with the Bristol chart. You can see the chart in the following link -
If your stool is Type 1 or 2 you can increase the dose. If it is Type 3 or 4, you continue with the same dose.
I hope that answers your question.
Let me know if I can assist you further.