what is your salt intake??
do you drink diet sodas?? (shitload of sodium)
PMS??

and are you drinking enough water... minimum of 64ozs a day...

How much water are you taking in in a day? Remember, if you tend to retain water, you need to drink more water. I know it sounds funny, but that's the way our bodies work.
Are you finding that you are really retaining around your cycle or is it all the time? There are herbal forms of diuretics that help immensely especially at that time of the month. Dandelion Root is an excellent diuretic as is B-6. The dandelion is very potassium sparing as well. There is also Uva-Ursi but I think I'd choose Dandelion over Uva Ursi.
And as Supergirl mentioned, get rid of the pop if you're drinking it.
Can you say BLOAT? lol....pop is the worst for bloating us.

Actually, I don't drink any soda pop, and I really watch the salt intake.
I'll check the Dandelion Root. Thanks for the tip...)