From your symptoms, it may be DVT .It is definitely possible to have DVT after a 5 hour flight with minimal movements. I would advise you to consult a doctor to undergo USG Doppler to rule out DVT.
You should know that DVT is recurrent. You have to develop a lifestyle to combat it. The prognosis worsens if you don't improve your lifestyle. As you also have a history of pulmonary embolism, there are chances you can eventually develop that again due to DVT.
I suggest you go for 30 minutes brisk walk every day. Go for yoga also if possible. It improves the circulation in your leg. Reducing the risk of DVT and secondly avoid sitting in one place for a long time, get up and walk every one hour once. Avoid having fatty food. Avoid exposing your leg to cold.
Use stockings if you want. It will help for your pain.