What Causes Fatigue,tender Breasts,light Headedness And Nausea?

Hi, Im 37 years old, fit and healthy. I generally have a regular menstrual cycle. I had unprotected sex with my partner nearly 3 weeks ago, and am now 2 days late for my period. I have tested negative so far for pregnancy, but have experienced the following symptoms:
extreme fatigue, very tender breasts, light headedness, occasional mild nausea, tightening of the abdomen (feels different to my usual menstrual cramps); a little spotting approximately 1 week ago. As my test was negative, I am assuming that something else could be causing all of this??