Pregnant?

So today makes four days late for my period. I am never late except a couple times maybe a day or two. I have been cramping for like a week and so far today no cramps. Is this a sign that AF is coming now or what? My nipples have been really sore the last three days but today is not that bad. I am definitely confused. I cant buy a test for two more days. I am 18 DPO..I dont want to get excited but i have no clue what to think. Help??