Hi there. This swelling in the legs and ankles sounds like Edema. It can be caused by a number of factors including heart failure. It can often be well controlled by Diuretics. I would strongly advise you to go to your Doctor without delay, as it needs evaluation by a medical expert, particularly given your previous medical complications and the description you give of your current symptoms. I wouldn't be hanging around, take action.
You need an evaluation by a physician as soon as possible. There are many reasons for swollen ankles, but they are not a side effect of coumadin.
Coumadin (Warfarin) is an anticoagulant (blood thinner).
Some people experience side effects from it, but most of them experience this during the start of the therapy and not after five months.
Anyway, very swollen ankles are NOT good. Also you unsteadiness should not be taken too lightly. Call your doctor asap.