Hi...I'm not on Colazal, but my UC original diagnosis was limited up into the sigmoid (so, not left-sided). Yes, there are some whose has continued upward....
You really should consider rectal meds...the constipation can very well be a symptom of low in the rectum inflammation. The Colazal should help the spread of it upward.
When was your last c-scope?
Are you having any other symptoms?
What type of diet are you following at this time and what foods seem to make it worse for you?
Are you using any fibre supplements?
You could consider to take a stool softener...I don't remember how many times a day it suggests, but that will help at least with the discomfort of the constipation.
You could also have IBS...which constipation is a symptom as well.
Can you not take rectal meds?