almost 16, no period :(

Hayley
So I'm almost 16, still haven't had my first period.
I've gotten discharge for just over a year, and my older sister and mum got their periods late too (sister got hers a few days after her 15th birthday).
It's so embarrassing not having my period now. Only about 3 of my closest friends know that I haven't had it (and are really supportive) but I feel like with everyone else I just sort of dis-include myself when they talk about theirs or I just listen or subtly change the subject.
Someone give me advice or
Hope, because this is just getting so annoying!!