What Can Cause Irregularity In Periods?

I'm usually like clockwork when it comes to my period. However, my period or what I thought was my period came a few days early this month. Not only that, but it was brownish pink and light. My periods are ususally heavier and this time I only used one tampon and it didn't even fill it up. The light bleeding lasted about 5 days. Now a week and a half later I started bleeding again. I can only see it when I go to the bathroom. I took a pregnancy test and it was negative. I am trying to get pregnant. My period was supposed to come on Feb 11 and they last about 4 days. My cycles are 26 days. Should I take another pregnancy test? Could something else be wrong?



Thank you