im 17 and ive never had sex before. i get my period on time everymonth but the last two months i got it on the 26 and ended the 31 wednesday i got a rusty colored spotting on my underwear and its been three days now and it hasnt gone away.... last time it was just one day. i dont know what this is.. im not in any pain, i mean my back hurts but it always does. please help i need advise!