What Could Cause Persistent Leg Pain And Swelling After Travel, Heat Exposure, And Prolonged Sitting?

Hi, I have leg pain and swelling. I sit a lot for my job, but was recently at a conference in Texas where it was very hot and humid. Flew home (4hr flight) and my legs swell up. That was very late Saturday night and they are still swollen and painful. my legs seem very heavy and awkward. I am overweight as it is, but never had this before except for an injury and it went away.