I Sprained My Ankle Badly About 15 Years Ago. Have

I sprained my ankle badly about 15 years ago. Have had pain randomly in it since. I am used to it swelling when I walk for a long time but recently I have noticed that when I touch the swelled area I can push it in with my finger and it holds the shape for a little bit before swelling up again. Once I ice it on and off for an hour or so it goes away. I was told by a colleague that it is fluid. Is this cause for concern?