Your problem of swollen ankles and feet have various possibilities like some very normal things such as excess salt intake, menstruation
(due to hormonal changes) and pregnancy or could be due to collection and trapping of fluid (fluid retention) in lower legs because of some dysfunction with organs like kidneys, heart, liver etc. But, as you have undergone blood, urine tests and also heart sonography
, these might have been excluded. It may also 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.
Hope this helps!