Long night shifts and constant coffee don't always mix well — a lot of shift workers end up dealing with stomach discomfort by the end of a 12-hour stretch, on top of being tired.
Drinking coffee on an empty stomach, especially multiple cups across a shift with irregular meal timing, is a common contributor. Add a vending machine energy drink or two and you're stacking sugar and acidity on top of that.
A few things that tend to help: eating something small before your first coffee of the shift, spacing caffeine out instead of front-loading it, and swapping at least one of those drinks for a format that doesn't add liquid or sugar to your stomach.
That's one of the more common reasons night shift workers reach for Neuchu — 50mg of natural caffeine per piece, no drink involved. You can find it here.