Hey Cloezone,
Yes you can masturbate on your period, however get yourself a nail brush for after as even if your flow is light it get's right up under your nails. You may want to put something under you like a dark towel or old T-shirt as sometimes especially if you masturbate internally it can make your flow a bit heavier or cause cramps. It's still perfectly safe to do it just seems to happen that way sometimes. Maybe you feel extra aroused at this time due to the hormones your releasing at the time of your period, usually a female feels most aroused about 14 days before her period is due, as this is when she is ovulating and her highest chance of getting pregnant, so her hormones send signals to her brain saying...'now is a good time for sex' I'm not advising you have sex lol not at all, masturbation is as good a relief just explaining why this can happen