What Causes Spotting Between Periods?

I am 30 yrs old and have had a normal period for as long as I can remember. My cycle started on 3/24 and is still going. The first few days were just as it should be. Around the 5th day it let up and seemed to be ending as usual. Since then, I spot a little everyday and do not need to use more than one panty liner. Should I be worried??