advise unclear šŸ™„

Alrighty, so I'm 15 about to be 16 tomorrow. About maybe a month ago now, I had un protected sex, but I was also on the last day of my period. None of us came, and we didn't really have time to do much. I haven't had my period since then. The <a href="https://play.google.com/store/apps/details?id=com.glow.android.eve">period tracker</a> thing on <a href="https://play.google.com/store/apps/details?id=com.glow.android.eve">eve</a> says I'm 8 days late. I asked my friend about it and she says "I'm young and my period has not regulated yet." I feel that because my period never comes when it's supposed to, but I'm just worried and I need a little more advise to make me feel better šŸ˜­