What Causes Lightheadedness, Dizziness, Nausea And Sore Breasts While HPT Is Negative?

Hello, I recently missed the depo shot last December and had been having unprotected sex... I m not sure if I may be pregnant or not but recently I have been feeling dizzy,light headed and nauseous at times and my Brest have been feeling a little sore...and I took a pregnancy test about two weeks ago and came back negative... could I have tested to early?? Or what could these symptoms be?