I think a lot of us did this. I knew gelatin was in gummy candies, but I ate yogurt and sour cream with gelatin for ages while calling myself a vegetarian. Marshmallows too, and cheese with rennet.
Luckily, there are good substitutes out there. If you like sour gummy stuff, Sour Patch will likely do the trick, and most organic yogurt doesn't have gelatin in it. Marshmallows are harder, but there are gelatin-free varieties out there. It's a good idea to read labels, even if it's scary to learn what's in your food sometimes (okay, a lot of the time).