Is my red wag platy pregnent?

If you have a male and female platy in the same tank there is little doubt that she is pregnant. If that is a picture of your platy you posted the link for there is little doubt she is pregnant. Platys are livebearers and are prolific breeders. Even if you do not have a male in the tank, if she has been with a male in the last six months she may still be pregnant, as livebearers can store spermatoza for many months and continue to have batches of fry long after there are no males in the tank. Beware, if you intend to keep the baby fry you should keep a watchful eye on your aquarium, it is not unsual for a livebearer to attempt to eat the baby fry after having them. The fry should be removed from the tank or placed into a seperate area. If you can, though, have the same water in the new tank to minimize the stress on the new fry. Anyway, congratulations on your upcoming clutch - by the looks of the pic you posted she is very close to dropping the fry. Cheers.