Usualy, during the first day of my period when I have cramps and bloating and back pain, and all that wonderful stuff (

), I also get these pains around my vagina and anus, usually only when standing and walking around- as if the muscles there are really tight and sore... this pain usually is gone by the second day of my period. Does anyone else get this? What is it from? This has been happening every time I get my period since I started getting my period 11 years ago, but for some reason, I'm just now starting to wonder if this even happens to anyone else...
Thanks!