You have my sympathy as this has been a problem for me for many years. In pregnancy it was not surprising and my feet and ankles "snapped back" after the babies were born, even if I did have stretch marks on my ankles. I think some of it is hereditary, my Mum suffered, and I have tried diuretics, had my heart checked etc to little avail. Years of standing as a teacher probably added to it too. Coach travel taking school trips abroad was quite hard as I had to travel in my shoes/boots as if I had taken them off I would never have got them on again.
So in summer I wear long floppy trousers and in winter opaque tight/ boots/ trousers again.
Sorry I have no advice to offer, just loads of sympathy!