how common is getting pregnant the day before your period??

I failed to have a period in July I got it on the 6th of this month the last time I had intercourse was on the 5th of this month about 5 days ago I started getting extreme body aches and pain extreme exaustion light cramping mood swings I crave food constantly but I eat a small amount and get sick and want food shortly after I know it's too early to test I was just wondering the likely hood of that happening or your experience any advice is much appreciated