I too am diabetic insulin controlled, (4 a day) and for years this has been an issue. Coke Light has now found it's way to Bulgaria, but Slimline Tonic is still unavailable.
Maybe like me you will need to change your drink whilst you are there.
If I am drinking shorts I go for Brandy and Coke Light and I have had no problems.
I found there was always something I could eat last year that was vegetarian. There's always pizza, eggs, soup, bread. And then there's always loads of booze and of course, that's vegetarian