Swelling in ankle for the past 3 to 4 years

For the past 3-4 years, I've had constant swelling around my left ankle that ebbs and flows. I don't know when it happened or if I injured myself. I've been also been doing high-impact exercises during this time, and my guess is that that might be the cause. There's been no pain; perhaps there was at some point but I don't remember. There is some tenderness above and on the right of the medial malleolus (see figure) – that too when I press very hard. There's no instability or inflexibility and I've continued to do the high-impact exercises without any trouble. I do experience extremely mild twinges when I go up and down the stairs very fast, but otherwise there's no problem.

The investigations suggested by my doctor – Vitamin D, B12, Complete blood count, Anti CCP, C-Reactive protein, TSH, RA factor – all were within normal range. I do have hypothyroidism, which I keep under control with supplements.

What could this be? Should I be worried?

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