No period??

S
I'm on the Pill, and my period was due to start Monday but now it's Saturday and I never got it. I've never had any problems like this - been on the pill for years and gotten my periods regularly. 
However, I did skip my period last month by leaving the last row of pills in the packet (although I have done this before & my period came normally the next month). Could this be the cause? 
No chance of pregnancy as I haven't had sex in 8 months 😭. 
Is there some other reason my period hasn't come?