Problem with repeating last action

[admin]

I've made a simple web page with mySQL database which enables user to add/edit/delete data from it, something like web addresor.
It does work, but if someone tries to reload the page using Reload button, my script repeat last preformed action, because variables have some values at that moment.
So if last action was adding new user, same user will be added again... that is a problem.

thanks,
Natasa