Far from expert here, but I was diagnosed as diabetic about the same day I was diagnosed with PDAC (2 years ago, age 58). Up until then, my A1C fluctuated between 5.6 and 6.0. After diagnosis, an endocrinologist prescribed me insulin, not trying any meds like metformin first. I don't remember what tests (if any, or just experience) guided him to that decision.

Now, 14 months post-Whipple, he had tested enough to confirm my pancreas is performing at about 50% in terms of insulin production and enzyme production. As a result, I take a nightly injection of long/slow-acting insulin, and with meals (if I remember) I take enzymes (Creon) and a fast-acting insulin injection.

I have reasonably good control, but it could be a lot better with some discipline. Unless my glucose is over 300 at bedtime, I don't use the fast-acting insulin at night, as I hate being awakened at 3am with a low blood sugar alarm. Exceptions are made if I know I overdid it with carbs at a late dinner. Pasta and rice seem to keep delivering sugar for hours after consumption.

When possible, I try instead to take a long walk before bed. Exercise is always good, and walking seems to lower my glucose by about one point per minute walked. So, at 3 miles/hour, 1 mile reduces it 20 points; 2 miles reduces it by 40 points, 3 miles by 60, etc...

My long-acting insulin is a Tresiba pen; fast-acting is a Novolog pen.

When I've had chemo (Folfirinox before the Whipple, Gemcitabine+Abraxane+Cisplatin after), they've always added some steroids (dexamethasone) as an anti-nausea pre-med; I also have prescription dexemathasone tablets for 1-3 days after chemo if nausea doesn't respond to my Zofran. That can really drive blood sugar up and seems to increase insulin resistance for a while. So, on the night before chemo, of chemo, and 2 days after chemo, I increase the long-acting insulin by 25%. If I'm eating "comfort foods" during that period, I have to be extra careful and use more of the fast-acting insulin to prevent some major spikes.

I got real tired of pricking my finger to test glucose, and my endocrinologist was very understanding. Had no problem getting a Dexcom G6 "CGM" (Continuous Glucose Monitor) prescribed and covered by insurance. Switched to the G7 when it became available. It updates every 5 minutes automatically on my phone (don't have to "scan" it). Biggest annoyance along with the 5-minute delay is the additional delay in seeing a response to consuming sugar after a low-sugar alarm at 3 am. It might still alert every 5 minutes for the next 20 before your sugar increases to a more normal level.

(Actually, the biggest annoyance is how loud the alarm comes through when my phone is connected by Bluetooth to headphones or a loud car stereo. I listen to music at pretty high volumes, and the when the high/low glucose alerts override it, it's like being hit by a truck.)