Yep! Similar story for everyone here with the vets and home testing, no worries.
Hopefully it evens out a little more. We usually give ProZinc 3 months of consistent dosing and dose adjustments before saying consider a switch to a depot insulin like Lantus or it's generics. Based on what I'm seeing so far you probably will need a switch eventually, but it's worth trying for another 1.5-2 months to see how he does.
As for the diarrhea - s boulardii is the best for it if you have trouble again. More info, dosing,e tc here -
https://www.ibdkitties.net/supplements/probiotics/
I buy Jarrow Brand s boulardii with MOS, but any s boulardii will work so long as it doesn't have added sugars or toxins