What Causes Irregular And Heavy Menstruation After Tubes Tied?

Hello...I hope you can help. I usually start my period the middle of the month,but in June I received it on the 28th! Tonight I have been on it now for 13 days! I had my tubes tied in 2002 and my periods have been like clock work since 2003. I'm confused and scared. It is a heavy period,but I'm not feeling any real discomfort. Any ideas of what could cause something like this to me?

Thank you and God bless,
C.