What Causes Delayed Periods With Sore And Swollen Breast?

As of right now, I am 12 days late for my period. I'm pretty sure I am not pregnant. My breasts are a little swollen and hurt on the sides. However, it feels like my stomach from the belly button down is hard, and it feels like if I press deep enough I can feel my uterus. Also, just recently I have been having problems pooping and have barely been able to. I have been very worried. What is wrong with me?