Hi braids,
Well, I've looked through as much scientific literature as I could get my hands on and I could not find any references to Tamoxifen and Diabetes or elevated glucose levels. Typically, the lack of any mention of this as a side effect means that if it was reported at all, it was a very rare instance, not enough to warrant a study.
This doesn't mean that your elevated levels are not problematic, but it does mean that the fact that it conicided with the initiation of your Tamoxifen treatment is probably coincidental. Jeanie's advice is very good advice; perphaps some short term long lasting insulin like Lantus would be helpful
Warren