I measure myself about twice a month. (Only because I'm super anal about my results).
But I NEVER meausre myself while on my period. I gain about 5 pounds and about 2 inches while on my period. I get extremely bloated. I don't suggest you measure during your period. You'll only get upset.
Like mentioned before, I also suggest 30 day shred. It is really great. I lost inches doing it. I also have started running on a daily basis.
Best of luck