Hello Faisal.



Brother I think you need to go through the contents of Computer Science and Physics. Read past papers (3 or 4 years would be fine). Then try to make up your mind.
As for me, I think CS would be a better option as you have a graduate degree in it and would help you a lot in Interview phase (InshaALLAH you will make it).

As far as other subjects are concerned, I think if you want to appear in CE2016 do choose International Relations. If you are in Lahore you can contact Ahtisham Butt, he is a fantastic teacher. He would surely help you a lot.
Then I think you can choose Hist. of USA because of it's lesser contents and redundant nature. It would take lesser time to prepare.
And Punjabi is a good option too as it is high scoring and easier to prepare.
This is my earnestly my opinion however it is up to.

And debate is open for better advises and opinions.