What Causes Delayed Periods With Nausea, Mood Swings And Tender Breasts?

I have tender breasts and lower back pain, getting headaches im nauseous im tired and have mood swings i started crying yesterday because they didnt have a yogurt in the vending machines in work and ive missed a period by about 3-4 days I had unprotected sex 10 days ago what could be wrong?