Is It Normal To Experience Delay In Periods Following Emergency Contraception Taken After Protected Sex?

Hi doctor I had my last period on April 14 ,on April 24 had protected sex with my husband,but out of doubt took ipill in 2 hrs ,but I missed my period the may month and this month am yet to get one I did more than 10 upt test after missed periods weeks apart all turned out negative Am used to Have regular period cycle until April Kindly help