Can anyone explain the light spotting?

I'm going on my 3rd day of a very light amount of brown spotting after bein a week late. I pee a lot, have sore boobs, backaches, some nausea when I wake up in the morning, cramps, diarrhea, gas & all I wanna do is sleep. I was like this when I was pregnant with my first child. All tests are BFN's if this is AF it's a very weird one.