For the past two years my bp average has been 140/90 i stopped checking for a while and now i'm average is 123/83 for a week now what can be lowering ?

It could be: better reading, less worry, more exercise and taking less calories, cut salt.

Many factors: Have you changed your diet- less salt, more fruits and vegetables? Are you exercising more? Are you under less stress? Have you lost weight? Limited or cut back on alcohol consumption? Any or all of these things can contribute to a lowering of your BP.