Once a week

It is no wonder I have to weigh myself once a week.  Yesterday I was nearly 7 lbs lighter.  Now I am 7lbs heavier.  So much must have happened in the course of a week.  According to the scale at home I am still at a plateau.  I am watching the Insanity workout, but am I physically able to do it?  I have tried the workout and yes, I am physically able to do it.  It isn't an easy workout but it is worth the money.  Right now I am doing not as much exercise as I should so I need to quit overwhelming myself with the exercise routine I am doing, or not doing.  I just quit too easily.  I almost did with my weight loss plan.  I can't afford to quit however.