If there was no trauma or injury, it can be attributed to being overweight, excessive alcohol intake, blood clot in the
leg,
leg infection and structural problems like veins in the legs cannot properly pump blood back to the heart.
If it persists, it is best that you refrain from drinking alcohol at this point and have this checked by your doctor for proper evaluation and to rule out heart, kidney, or liver failure. Take care and do keep us posted.