My boyfriend and I had unprotected sex last weekend (the 16th, today being the 24th) he didn't fully *** inside of me; regardless there was still an amount of it in me. Problem is this was right in the middle of my cycle(period due the 31st)and by the time we realized this it was too late for plan B. I'm 18 and not on any birth control, what do you think the chances are I'll be pregnant?

It depends on a lot of things, including how much semen got into you, and how fertile you were at the time, but I think you have to consider that you had unprotected sex and work on the assumption that you may be pregnant. Do a home test on the day you expect your period.