my period came down twice in one month

Hey my period comes at the end of one month and go up at beginning off the next month. My period never came down at the end of December 2013th. My period came down on the 13th of January and up on the 21st. My period was light and the color was pink and light brown. It didnt come in my pad much at all. How I knew it was down is when I wipe my self. On the 27th of January it came back down and I didnt know until I wipe my self from using the bathroom that evening. Its not coming down in my pad but its light pink and light brown. I took a pregnancy test and its negative. I been taking a pregnancy test since December. I been having heachaches, lower back pains, and I been sleeping alot. I want to know whats going on with me. I tried buying pregnancy test and it's coming out negative