Am on birth control pills,for 2nd month,i still have 7 pills in pack and i had unprotected sex yesterday i can't risk being pregnant, do i take an ec?

You can: But if you're taking all your pills on time, your chance of pregnancy is very low (around 3%). It sounds like you're in a part of your cycle wherein you're very unlikely to ovulate, therefore pregnancy rate may be even lower than 3%. If you decide to use emergency contraception, I recommend discarding this pack and starting a new pack within a few days.