Watch Weight

Below is a chart tracking my weight from late Nov 2007 until Feb 2011.  I started out at 205-210, now I am about 185-188.  At my heaviest, in 2004 and 2005, I was about 230ish.   I stopped drinking regular soda and went to diet and that lost weight almost immediately.  I also started duathlons in 2006 and that resulted in some major weight loss. 
I cannot get below about 186.  I have been trying to get under 180, but I have not been able too.  Probably because I like beer, burgers, and pizza.
Over the last couple of years I have tried to weigh myself every two weeks, two days during that week.  I go to the bathroom and then weigh myself nude on the scale, before getting in the shower.  Hopefully, this adds some consistency.