What Causes Irregular Periods?

hi m 27 year old and m having irregular periods before even twice in a month and when i had first sex with my boyfriend for the first time ever in my life i started having my periods on time on same date every month.but now i have missed my periods for 6 days after having unprotected sex while during my second day of my period and 4 days after that.now m having bit pain in my lower stomach,body pain and white discharge also and sumtimes it feels that m going to have my periods but it does not,eles everything is fine with me.please suggest me that m i prepnent or not?