Suggest Remedy For Delay In Periods

I had sex with my boyfriend. Please see below different dates 12 Feb 2011 - My Last period started 18 Feb 2011 - I had sex; he did not ejaculate but may be premature ejaculation 19 Feb 2011 - I took i-pill (emergency contraceptive pill) 27 & 28 Feb - I had bleeding (little heavier) 12 March 2011- Next period was expected (28 day cycle But No period till date (23 March 2011)Urine tests conducted on 14 March 2011 and 21 March 2011 are NEGATIVE Need expert advice YYYY@YYYY