Hi @bluehedgehog and welcome to Mayo Clinic Connect.
You might benefit from the experience shared by members in other discussions who posted about subtotal colectomy, so I would like to invite them to the conversation.
@ellemorgan - https://connect.mayoclinic.org/comment/666834/
@nobletype - https://connect.mayoclinic.org/comment/72874/
@bermuda56 - https://connect.mayoclinic.org/comment/160240/

And here is an NIH article with helpful information: "Currently, a total colectomy and ileorectal anastomosis are known to be more successful than a subtotal colectomy and ileo-sigmoid colon anastomosis [20]. Some remaining sigmoid colon can cause a recurrence of constipation, but anastomosis below 7-10 cm from the anal verge can produce diarrhea and fecal incontinence." -- Surgical Outcomes after Total Colectomy with Ileorectal Anastomosis in Patients with Medically Intractable Slow Transit Constipation: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3180598/

It looks as though it has been just over a month. When did your doctor say you would start to see improvements?