Your problem of swollen ankles and feet have couple of possibilities. It may be due to formation of blood clots
in the the blood vessels (deep veins) of legs obstructing blood flow into the heart called deep vein thrombosis
(DVT). Usually, this is caused by prolonged sitting or standing. This can be diagnosed with investigations like Doppler Ultrasound. If neglected there may be complications like embolism
Your problem may also be due to some other possibilities due to collection and trapping of fluid (fluid retention) in lower legs because of some dysfuntion with organs like kidneys, heart, liver
etc. But these chances are less as you are previously healthy. Please consult your doctor to rule out all the possibilities.