How long have you been on the Metformin? I’ve been on it more years than I care to remember (long before my T2 for something not diabetes related) I still very occasionally get a tummy upset.
I agree it’s a very common side effect of Metformin but getting a bad tummy may not always be down to just the medication but sometimes it’s hard to look past that with the rep that met has.
I’ve found that certain foods can upset me & it’s more what I eat than the medication, fried mushrooms on their own, if I eat too many of those, i love them on low carb toast, that can trigger me, I’m fine with them in food in general such as sauces, curries, even as a side dish on a meal such as a breakfast, but on their own no. Hot chicken just on its own does it for me too, any other time is fine but eating hot roast chicken just in its own, again it can trigger tummy upset.
Maybe keep a food diary to see if there’s a pattern to your diarrhoea? If it’s only happening a couple of times a week you may have a trigger food or something else is triggering it? Usually when it’s a side effect of the meds it is all the time. I was also advised by my GP that it’s safe to take Imodium when I need it, I was on Gliclizide at that time (not now) but not insulin so maybe check that it’s ok to take Imodium first with your pharmacist or GP