What Causes Delayed Period After Taking I-pill Followed By Unprotected Sex?

hello , i had an unprotected sex with my boyfriend on 27th of july...and that was the fourth day of my periods. i had a doubt of being pregnant so i took an i pill within 12 hours of sex.then bleeding continued for 3 or 4 days...... after that we had unprotected sex thrice on interval of a week...like on 5th aug..then on15th aug ...then 23rd aug..but we both realized nthing wrong happened to i didnt took i pill again as i was nt in doubt. but till now i dint get my periods... is there any chance of being pregnant or its just delay due to i pill? n pls tell me wat should i do?