This is always the best approach to sex.
This will only cement the stain in the sheets.
Orgasms relax the uterus, climaxing increases blood flow and releases endorphins.
More in Birth Control.
If you don't want to put anything in your vagina you could use a dental dam.
This is due to your libido changes that happen throughout your menstrual cycle, as a result of hormonal fluctuations.
Take it from me, as someone who's accidentally left a tampon in during slovakia sex and lost it for a few days until I finally fished it out in the shower, it's not a pleasurable experience.
Though period sex can be a bit messy, it is safe.
Taking Charge of Your Fertility.