Pregnancy

So I have a question... my boyfriend and I are wanting to conceive our 1st child. I got pregnant in 2014 and had a miscarriage. I literally got pregnant out of the blue. I never know when I'm ovulating because honestly my period comes whenever it wants to.

So I'm wondering, he gets home tomorrow and will be here for three weeks. My period calculator says it's coming in 2 days --- but I've never been regular so idk how accurate it will be...

What's the likelihood of me getting pregnant anyway? If we get it on the day before it's supposed to come.