Midol ? ......J/K
When I get a sour stomach I try a "reset" by using activated charcoal - 1 to 2 servings, note this will turn stool black and hard. This cleans out the stomach and removes any out of balance bacteria. Then I use a cycle of Glutamine + FOS + acidophilus + any natural probiotic like in real yogurt or drinks.
Stress, is a major component as well.
As already mentioned an allergy or intolerance - go natural & avoid gmo, look for sources of chemicals in your diet, public drinking water that's treated, spectracides on fruits/veggies, some soaps, shampoo's, deoderants, can all contain toxins to the body.