Most probably your whey protein product is made with whey concentrate, which has lots of lactose in it. Lactose will cause stomach issues for many people, and it seems like you are one of those. Therefore, you need to find a protein product that will be made 100% with whey isolate, which is the purest form of whey protein, as it has no lactose in it. For instance, Wheytobuildmuslce by N2BM only has the isolate, and there are no additives at all, so it is as stomach friendly as it gets.