Period hasn't come

AJ • LeFt YoU wAnTiNg MoRe ;)
I take dianete pills, and recently I was on holiday, so to not have my period I had one packet 21 days, and an additional 9 days after that too.
But I have returned home, and stopped taking them for 7 days (been 3 days) and I haven't gotten my period yet?
Why?