What Causes A Missed Period,sore Nipples And Negative Pregnancy Test?

Hello, I am 29years old female. I have P.o.s.. I am going to get my hysterioscopy. And leproscopy done early next month. Now, I missed my period on February 15th, I did had unprotected sex beginning of February. Recently I started feeling dizzz all the time, faint pain at lower abdomen, rigid lower abdomen, sore nipples, , heart is beating really fast,feeling sick sometimes.I went to see Dr,have done pregnancy test. Which is negative.What it could be? Really worried need help please!