I had a tubal ligation 3 and a half years ago, always had regular periods since, but now I'm late

I had my tubal ligation done almost 4 years ago (4 years this coming September 2009). My periods ahave always been every 28 days before the tl and after. My lmp was 3-10-2009 and I was due to start on 4-06-09, and as of yet I have seen nothing. Usually before my period I get moody, irritable, etc., but not now. I often have cramping days before I start, but really nothing to complain of, with the exception that I keep feeling like I need to use the bathroom to do number 2 and lower back pain. Usually when I have my period I have back pain but not the feeling like I have to go part. My stomach is a little bloated and feels a little junky like I'm going to start but nothing yet. I am affraid of tubal pregnancy. My husband and I do have unprotected sex, because we figure we won't get pregnant. Should I take a pregnancy test, and if so when? Any advice or comments are welcomed. Thank you.