What Causes Painful Periods?

i have had unprotected sex twice ruffly 10 days before my periods were due the day before they were due i had slight bleading but it was far to light to be my period 5 days later i aventually recived my period and i havent had sex since my last period however my periods are due on saturday but ive got these symptoms a few weeks before now ive been getting constant period pains,, on and off headaches and sometimes feeling a bitt sick ,,i just keep thinking i might be pregnant but i dont think i can be as i never skipped a period so what can it be?