Hi! I'm a 19 year old girl, I am sexually active. My breast have been tender and sore for about a week now, and my nipples are sore and erect also!! I have also been craving salty foods and lots of water, and also urinating more frequently than normal, and having lower back pain. I thought the last four symptoms could have been because of a kidney infection possibly, but it doesn't explain my breast.. Could I be pregnant? I have taken an at home pregnancy test and it came back negative, but I don't get my period until the beginning of each month.