بسم الله الرحمن الرحيم
(1) In case you keep fast, you fear high increase or decrease in diabetes and unbearable problems then you are permitted to miss the fast. But you should perform qaza of these fasts in winter time when the days are short. And in case it is very much difficult for you to keep fast continuously then you should keep it with a gap of one or two days. In case you have no fear of unbearable problems due to keeping fast then you should keep fast in the month of Ramadan and should not miss them.
(2) Recite the following dua extensively, in-shaAllah your problem shall remain within control:
أَذْهِبْ الْبَاسَ رَبَّ النَّاسِ وَاشْفِ أَنْتَ الشَّافِي لَا شِفَاءَ إِلَّا شِفَاؤُكَ شِفَاءً لَا يُغَادِرُ سَقَمًا (مشكوة شريف ص 389 بحواله سنن ابو داؤد)
Allah knows Best!
Darul Uloom Deoband