Period is 15 days late & pregnancy tests are negative

Soooooooo my period is now 15 days late, I have taken 5 pregnancy tests (all different brands) all with my first pee in the morning and they all have been negative. Not pregnant. My mother in law still thinks that I am pregnant, and my best friend keeps telling me that some woman don’t get a positive pregnancy test til 7 weeks or even at all. I have been taking prenatal vitamins the last 4 days just in case I am. On the night of the 13th day my nipples were more sensitive then they have ever been. But no cramping that I can remember. On the day my period was supposed to start I wiped and it was a little, the teensiest bit, brown/red, but that was it. I’m wondering what this could be. Was I pregnant and miscarried very early? Could I still be pregnant? Is my period just going funky for no reason? (I’m not overly stressed) just wondering what could be happening, thanks for the help.

EDIT:

I posted this about an hour ago, since then I have gotten out of bed to make breakfast. I was in the middle of buttering my husband’s toast and all of the sudden I felt like I needed to barf... I went and sat down and it’s been about 35 minutes since then (and I’ve showered to cool off) and the feeling still lingers. For past periods I have NEVER felt nauseous, sooooo I don’t know what to think about this. What do you guys think now ? Help please.