Hi I am 19 and sexually active I have been in a long term relationship for 3 year and have unpretected sex. I am currently on the pill and have been for 4 month now, last month I was 9 days late for my periosd and then had a brown discharge for 7 days,I did a HPT about 15 after my period and it was negative, I was due to get my period on the 18th of this month but still nothing, what could this be my period is usually quite regular as from being on the pill.

(I did a HPT about 15 after my period) about 15 days after my period was due