I Am 15 And I Havent Started My Periods Yet.

I am 15 and i havent started my periods yet. I know it can happen later for some girls but its meant to be about two years after you start puberty. I had boobs at 10 and hair at 8. So i should have it by now. Also my 11 year old sister has started hers. My mum had struggled to get pregnant so i am worried about kids too. So should i go get myself checked out?