What Causes Dizziness And Sore Breasts?

I am getting dizzy shaky spells at least once a day, as if it were low blood sugar. I eat well, never skip a meal and snack a lot. I had unprotected sex with my partner on day 4 of my cycle. Is there a chance I might be pregnant? If that were the case, we would be over the moon. But I thought that during your period you couldn´t fall pregnant. I have all the other typical PMS symptoms (enlarged and sore breasts, mood swings...etc.). Thanks for your help