Need help understanding why !

Laibah

So I haven’t had sex since May 8 and my period was supposed to start on the 18 of June and I’m five days late and I just don’t see any signs of it coming anytime soo I even took a test just to make sure n it came out negative but I’m still stressed as to why my period is so late if anyone can guide me towards some knowledge on this that wud be really helpful !!!