Hi there, your doubts are valid to a certain extent. In case of both lower limb involvement of swelling one of the few disorders one needs to look into are those of the heart, kidney and the liver.With regards to the heart there is poor inflow of the blood from the veins and that causes pooling and extravasation of fluid which leads to edema and swelling. In case of liver and kidney problems it mainly is related to the low blood albumin levels which lead on to disturbed osmotic balance in the body. There are specific tests available for each for which you need to visit your doctor before you get them done because these diagnoses require a good physical examination before any tests can be further ordered. Also an important cause could be abdominal tumors. But i would suggest you get the required investigations done before jumping to conclusions.