What Causes Burning Urination And Cuts In Perineum?

hi, i seem to get these little cuts between my vagina and bum, i dont think its due to sex, as i last had sex 2 weeks ago, i went to the toilet earlier today and as i began to urinate, it must have torn, and boy did it sting, what could it be? and how can i prevent it, it happens at least once or twice a month, also to add, i have just begun my period today.