It sounds like your primary care doctor
has already starting working you up for the more serious causes of swelling in the legs. One of these is indeed a deep vein thrombosis (DVT), or blood clot in the veins of the leg. If this test was negative, then this is very reassuring. Additionally, your doctor will want to rule out any problems with your heart, such as heart failure or high blood pressure
, which can also cause swelling in the legs.
Assuming all of this testing is normal, then the most common non-serious cause of swelling in the legs is venous insufficiency, or varicose veins, caused by degeneration of the veins in the legs and their ability to carry blood back to the body. This typically causes exactly the pattern of swelling that you are noticing, that is gone in the morning and then worse at the end of the day.
Most of the time venous insufficiency can be treated with simple measures, such as avoiding salt, elevating the legs, wearing compression stockings, and, occasionally, taking a diuretic medication. More severe cases may need referral to a surgeon
Your primary care doctor will be your best ally in figuring out what to do next!