Am I pregnant or is Aunt Flo coming?

My husband and I have been TTC for 5 months now. Every time around my period I start really paying attention to my body (which I think has been reading into it sometimes.) I am due for my period in three days and I have been cramping pretty good. I took a first response pregnancy test yesterday, which was negative. So- I thought... try again next month. However, I have been feeling nauscious and tired. The cramping feels like my insides are being stretched outward and constant. Any thoughts? (we got pregnant with our first the first month)