What's up with my boobs?

My period isn't due to start for another 4 days but starting just a week after I ovulated my breasts have been swollen, heavy, severely sore, tingly, my nipples feel sensitive, and veins are promenent. Also my stomach has been a mess with constant diharia or constipation. I took at home pregnancy test yesterday and the results were negative. Could this be an early sign of pregnancy? Just too early for a test to pick up? Help! We're trying for our first child!