URGENT!!!! i need as many responces as possible! what is the percent of me being pregnant & how do i know?

me & my boyfriend have had a lot of sex within the past 3 days without ANY form of birth control. the first two days we used the pull out method, but the third day i let him come inside of me. what are the chances of me getting pregnant? also, i get my period irregulary.. always have! i get my period about every other month. the last time i had my period was around may 14th, but i missed last month. how do i know when i'm ovulating this month?