A tampon is used to stop the flow of blood that connects with menstruation and reflects a desire for certain natural experiences to be tidier and cleaner than they naturally are. What flow in your life are you trying to stop from moving naturally because of some sense of shame or inhibition?
There is an interesting use here of something phallic to alter something vaginal; look for where you are switching out a masculine approach when a feminine one would be more authentic.
[1]Tampons in dreams signify that you are having trouble accepting your feminine side. Also see “Menstruation.”
[2]