GiRl PeRiOd .....HeLp!!!!?

i havent started my....ya....and my b-day was jan18 and most of my friends got der period a few months afta they turned 12 but me im still alone.....evry1 of my friends has started and dey was sittin around talkin bout it and dey asked me if i had started and im like no and they keep buggin me sayin anyday now...any day and im nervouse cuz my older sis *29* said our mom tells evry1 she kno's lol....im just RLY nervouse bout startin and its kinda awkweird talkin bout it so....yaz.....HELP!!!!!!!!! o ya and my stomache's been hurtin sum low so ya dats it :l