Surgery and (relative) inactivity during recovery can increase the risk of blood clots forming in the legs, even if precautions are taken in the operating room (such as active anti-embolic pressure boots or leggings). Regardless of when the clots formed, as you resume more normal activity levels, the clots can partially dissolve and can "break off" and then travel in your blood stream to your lungs. (In rare cases of persistent congenital hole in the heart between pumping chambers, clots could also travel to the arterial circulation and cause a heart attack or stroke.) These are risks that any of us undergoing surgery will have, but other risk factors can increase the likelihood of blood clots forming, even in non-surgical settings.
These include genetic or inherited clotting disorders such as Factor V Leiden (search "Factor V Leiden" on this site for my answer about this topic), obesity, hormone use (birth control), smoking, excessive immobility such as airline flights or long car rides, and a host of possible hematologic abnormalities that can show up in the form of clots and pulmonary emboli.
Appropriate responses to your diagnosis are Hematology work-up, blood thinners, and possible other recommendations specific to your individual situation. I'm glad you're doing well; this is something that can happen to any of us or any of our patients, even without surgery. Good luck and continued best wishes!