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You probably have Varicose veins
. It is a permanent dilatation of the veins due to chronic stasis which can occur due to prolonged standing as one of the causes. Is this swelling on both legs or just one. The other possible diagnosis can be a Venous malformation. Both these can cause swellings in the area. The wall of the vein is weak which is why the swelling is increasing. It would be best to get it treated otherwise relatively minor trauma can cause a huge blood loss which won't stop if the vein is damaged. You can approach a surgeon who will be able to remove this damaged vein by very small skin incisions
all done under anaesthesia. Nothing to worry.