period 5 days early!!!

Yesterday my boyfriend asked why I was being all moody. I had a breakdown while we were driving in the car. But I have had no period cramps. Yesterday my boobs were killing me. I didn't even notice I was acting all moody until he sad something. Have had some cramps today anyway today during the day I went to the bathroom and started my period it's watery and a some blood clotting. Has this happened to anyone else? And why is it 5 days early?