Typically a blood clot that is formed in the lower extremities (also known as a deep vein thrombosis, or DVT) presents with enlargement/swelling of only one leg. It is much more common to have a DVT affecting one leg rather than both at the same time, though it is not impossible. Typically a clinically significant DVT will cause swelling that rises up past the ankle and involves at least a portion of the lower leg beneath the knee. Clots that form higher up towards the waist can cause swelling that rises up into the thigh, if the clot burden is severe enough.
If there is not enough blood getting to the feet, then a person would likely experience skin color changes on the feet, a sensation of numbness or tingling
or frank pain in the feet, and may have difficulty moving the feet.
When swelling is limited to the feet and both feet are affected, there is the possibility of venous insufficiency to consider. In this condition, the veins in the legs start to lose their ability to return blood to the heart, making it easier for water to seep out of the vessels and into the skin. This typically occurs after a long day on one's feet, and gets better with elevation of the legs.
Because the cause of your feet swelling is not completely clear, you should see your primary care physician
who will be able to conduct a thorough history and exam and come up with a diagnosis.