Go to the ER for fluid retention, possible blood clot, or heart issues (circulation). I had the same issue... my legs swelled up to elephant size and I was in the hospital for 5 days. They thought it was post partum cardiomyopathy, then it was blood clots, then it ended up with my body being unable to handle the extra fluid left over from the baby, which my body was having a hard time absorbing.
Most women don't know this, but the body ups it's blood volume/fluid by 45-55% during a pregnancy in order to balance your circulation needs with the baby's. Once the baby is gone, you have all that extra fluid volume to loose or absorb...