When I was a child and had a stomachache, this is what we did to cure it....
1/2 C. water
1/2 tsp. baking soda
1 Tbsp. +/= lemon juice
You put the baking soda into the water and poured the lemon juice in as you stirred. You actually added as much lemon juice as was needed in order to make fizz up a bit. Once it fizzed, you were to drink it immediately. It tastes rather nasty, but I've tasted worse, and it really worked.