I had my normal period on 20th May. Has sex with my husband on 1st June, however unfortunately the condom slipped. To be on safe side, I had an emergency contraceptive pill the next morning. That month I got my period on 12th June (about 8 days earlier than my normal period), and it lasted also a few days longer than my normal period. Now, today is July 15th and I have not got my periods until now.  I took a test but it is negative. I am worried and confused. Is this normal? Should I expect my period to start 30 days after my last period (i.e by 12 July) or my normal time (i.e 20th July). Please advice. 

P.S. I have fairly regular cycle otherwise. Thansk!