Period questions...? (Basic questions)?

Hi so im 11, 12 in like two weeks so i dont think im too early to get my period. I didn't have too much blood in my carefree-btw a carefree is like a thin pad.. i always wear it and today morning i looked and it had brownish red blood! so i think i got my period. and plus i slept for 13 hours and one of the period symptoms is tiredness so im pretty sure i got it..anyways i dont feel it at alll! im actually really happy about the fact im not getting cramps or anything like that...anyways am i always gonna not feel my period? or am i probably just lucky this time? also how long does a period last and how often do you get it?And my sister two years older than me hasnt got hers yet..? is this abnormal i got mine first? thank you(: