It is a common thing. If it's just happening occasionally with you, you might want to note what types of food you're eating when you get the 'tablet tummy' as we call it in our house. For me, after a few weeks of starting to take metaformin, my stomach got used to it for the most part, and now only certain foods trigger the upset, like seafood, which is a shame as I love it. And strangely certain types of salad leaves that you get in the pre-prepared bags. :?
Vicky