Left leg has clot but still has not enlarged. Whats up with this?

Presents variably. Commonly, blood clots cause pain and swelling but sometimes they will only cause one or the other. Occasionally, they cause no symptoms. If a blood clot is small and in what we call calf veins, you might only get pain without swelling. If the clot is only blocking part of the vein, but not all of it, you also might get no swelling.