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I presume you mean you have whole body swelling. With a history of cancer, the commonest cause could be anemia. Generalized body edema can be very serious. It can be due to severe anemia, a failing heart, serious kidney disease, liver failure, electrolyte imbalance, polycystic ovary, low protein in the blood, and disorders of adrenal gland. This is something for which you must consult a doctor ASAP, preferably an internal medicine specialist. Metallic taste in mouth can be due to any of the above conditions or due to any medication you are taking.
Hope this helps. Take care!
If the swelling is in the arm on side of breast cancer not whole body seek advice for lymphedema. This condition can begin many yrs after original problem.