What Causes A Delayed Menstrual Period While On Birth Control Pills?

Hi I hope you can anwser my question !! I have been taking ovral 21 birth control for over 3 years and thay stoped making them and changed it to portia 21 so ive been on those for 8 months now and this month i missed a few in my 1st 2 weeks and say i forgot to take yesterdays pill i would take that one along with my next pill so i missed my peroid and i was spsoe to get that on feb 10th and never got it! so i started a new pack should i stop those to get my period and start taking a new pack when i finshed my peroid!! Thanks