its usually by the time your 21, you need to go, it lasts maybe a whole idk 20 secs, I'm like you with the getting the period once every three months deal, went to a doctor about it (before I was out), and they did a hormone test on me, turned out my testosterone was higher than normal in girls (go figure), and that i had something called pcos. Basically if I wanted kids, would take a few tries or need to go to a fertility clinic (not that big of a deal now). They try to counter act it, by giving you birth control pills cause it has estrogen in them, say no if your going to transition. Hope this helped.