It is possible that a blood clot in one of the deep veins of the legs is preventing blood from flowing back into the heart. This will cause fluid retention in the part of the leg below the clot. This condition is called a DVT (Deep venous Thrombosis).
You need to take a test for a substance called D-dimers. These are found in people with thrombosis. You also need earlt treatment as the clot can get dislodged and travel to your heart and launs with dangerous effects.
Please see more about D-dimers here:
I hope this helps.
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