Yes, regarding UC...it depends on where it's limited to...and that would be in the rectum.
Yes, you could have IBS - C. That also would mean that the rectum is controlling the shots.
You will need a c-scope to help determine what's going on...with biopsies to determine if it could be UC or still ischemic colitis.
SIBO wouldn't be an issue creating constipation in my opinion.
I also see you have type II diabetes.
Do you have a gastro doctor, and have you asked questions and are you having further testing?
I'm posting a link for Ischemic Colitis for those who are interested.
/en.wikipedia.org/wiki/Ischemic_colitisq