I had unprotected sex the day before I ovulated (Saturday). Since Sunday I have had cramps, and am nauseous 100% of the time. Most of the time it's mild, but it can get bad to the point where I feel like throwing up. I also have had very minor headaches here and there, and am more tired than usual. Am I tricking my body into thinking I'm pregnant? Or is it possible to have symptoms this early?