Is there any pattern other than when you first eat? By that I mean is there also a particular type food you have eaten that maybe part of the equation. I'm thinking food intolerances , lactose, gluten or fats or any of the FODMAPs . I'm intolerant of lactose, gluten and fats. Lactose will cause me to have IBS , Gluten because I'm have coeliac, and high fats give me nausea and IBS. Serious diarrhea can ensue with all three. Keeping a food diary sounds like a good step. I did about 9 months of very low carb several years ago, I did not have any ill effects from the diet other than losing too much weight.