Suggest Remedy For Light Periods And Soreness In Breasts

im 16. about 5"4 weighing about 134 lbs. i had unprotected sex on the 8th of october and had my period the 15th. it was very weird because it was light. with no blood clots and would stop for a night or half a day then a little blood would come out. sometimes brown. i usually have blood clots and it usually goes from heavy to light bleeding. my boobs also hurt before i start my period but this time they hurt before during and after and still hurt. i took a preganancy test but it came out negative. what could it be?