Tampons themselves cause infections, tampons are bad for vaginal health and commercial tampons (e.g. Tampax) are the most harmful of over twenty different menstrual options. If concerned about infections you may want to consider a safer menstrual option such as menstrual cups. Tampons themselves are absorbent wads of material being put into a moist delicate area where bacteria breeds thus causing vaginal splitting and giving bacteria and yeast a good place full of nutritious menstrual blood to multiply upon. Commercial tampons are made from super-absorbent materials that add to the issues mentioned in the first point, but also contain bleach and chemicals that are unnecessary and contribute to infections by affecting vaginal PH, in turn affecting natural bacterial and yeast balance. As for the olive oil, that in itself shouldn't cause an infection, many women use it as a natural lubricant, in fact it is beneficial because it is slightly antifungal, although the issue I'd see with this is that because tampons cause vaginal splitting olive oil may cause some discomfort.