Hi dear Contraceptive
pills are effective in controlling child birth only if they are taken regularly and at fixed time.
Irregular intake causes breakthrough bleeding
and on the other had gives you false sense of security against pregnancy
So, if after taking pills irregularly you have missed periods than it is quiet possible that you have conceived. Stop the pill immediately and get pregnancy test done immediately.
Also, my advise is to use some other means of contraception
in future which can be followed easily