It sounds like you had something called a 'vaso-vagal' episode. This leads to symptoms of feeling faint, clammy, nauseated and sometimes even passing out. When you put a tampon into the vagina, it can touch your cervix, which is at the top of the vagina and closes the path to your uterus (womb). For most people, this isn't an issue, but some people have quite 'sensitive' cervixes and have a vaso-vagal when there is pressure put onto their cervix. Try using a smaller tampon and make sure you put it in whilst you are in a place where it would be safe for you should you faint (e.g. on your bed). Make sure your mum, dad or sibling is close by to help you out should you have another episode and pull it out straight away if you feel unwell. I suggest you see your Dr to discuss the options. Good luck!