Not all whey isolate is the same. Lactose upsets my stomach. Even though it says isolate, it can still have lactose in it, which I believe is a sugar. I have found that this product.
Isopure Zero Carb Protein Powder, 100% Whey Protein Isolate, (unflavored)
It does not have lactose (and zero sugar) and causes me no problems. Other whey products do cause issues for me.