I have three different kinds of Stevia at home. I have the drops which are fairly mild tasting. Then we have little pills that come in a flip top container and look much like a breath mint - they are supposed to be one little table = I tsp. of sugar. Then I have a loose Stevia that is very sweet. I use only 3 - 4 drops of the liquid when I drink decaf tea or coffee - my husband uses 1 tablet in his decaf tea and/or coffee and he finds it sweet enough for him - and he used to use two heaping teaspoons of sugar in each and every cup. Possibly you did get a "bum" batch of Stevia because we find our very sweet. I barely use the loose-ground Stevia because it is soooooo sweet, it is difficult to regulate.
Just on a personal note, I used Stevia because it is natural and not made of chemicals and leaves no aftertaste in my/our mouth. I am going to try substituting Stevia in some of the recipes, replacing Splendia and some of the others in the low-carb recipes.
I am really sorry to hear this didn't pan out well for you.