What Causes Delayed Periods With Back Pain And Watery Vaginal Discharge?

My period is a week late. My periods have always been regular and last around 5 days. Right before I was suppose to start I was having terrible back pain, which didn t strike me as strange because that s usually one of my pms symptoms. My breast usually swell and are very tender as well. Which this month, they did swell, and started to become tender, but then the tenderness went away. That I found strange. Two days after my missed period, I started having clear, watery discharge. Since that day I ve continued to have it. Now a new symptom has arrived which is pressure in the lower abdomen. It doesn t so much hurt as it is just uncomfortable. I also took a pregnancy test today that came out negative. Help! Was it too early to test? When should I test again? What else could cause my period to be late?