What Caused Delay And Then Bleeding Between Periods After Unprotected Sex?

i am 24 year old married woman. i had unprotected intercourse with my husband and that was our first unprotected one. i used emergency contraceptive pills in the next morning and the time gap was 10 hours. i usually have irregular periods and the length is normally of 7 days which is normal for me. but even after one month of the intercourse i didnot have my period. then i used pregnancy test tool and that was negative. now after two months i had my period. it was okay till 8 days but it started again after 12th day. i dont know what is happening. this time i had severe pain on the 2nd and 3rd day of period and extreme blood loss. why is blood seen even after 12 days of my period?