I would try another brand of tampons. They all react a little differently, and form to shapes a little differently.
The only brand that I can count on to not leak (unless it fills up!) is Kotex Security. I use all three of the strengths (reg, super and extra). The Tampon brands never expand enough to fit my body, and they always leak for me, no matter what absorbancy I tried, or how often I changed.
Just experiment with some different brands, and be sure you are putting them far enough in. Sometimes, we tend to not push hard enough, and the tip can actually be showing a little - that is a guaranteed "leak" waiting to happen!
Contrary to rumors, you cannot get one lost inside of you! If you lose the string, just "squat", and it will show back up!
The feeling of being cleaner when compared to pads is amazing, so don't give up yet. It isn't you, it is the brand you are using. You will find the one that fits your body the best, then just stick with it. (and always wear a pantiliner with them anyway - even the best can leave some marks sometimes, esp when you are past due for a changing.)
[This message has been edited by Katymom (edited 08-25-2003).]