Hello mam, thanks for trusting health care magic.
There are negligible chances of pregnancy
while on pill if you have been taking them daily at same time.
But ever since you have deranged periods this time you need to do a urine pregnancy test and if it is negative then nothing to worry.
In case the abnormality persists then get a pelvic ultrasonography
and then vsit your gynecologist
In case you have further questions you can consult me on health care magic forum and i will be happy to help
Take care and wish you all the best.
Dr Manisha Jain.