Why do i do this to myself every semster

I just did  a 5 page research paper that i have known about since the first day of my class!!!  Oh by the way its due tomorrow.  I can't figure out every semester why i start to procrastinate as the semester goes on?  I start out every semester all ready to do work and not procrastinate and that last about a month then i slip into procrastination mode. If anyone has any advice for me please help me out!