Hi...I believe the cause for weight gain in your case is probably secondary to the sedentary life style... Every one knows that weight reduction comes with good and regular exercises mixed with healthy diet... But the problem is starting it and more importantly  sustaining it... Once you learn how to solve this problem, you will notice results.  You can start at office with  exercise like using stairs while climbing, walking around during presentations and breaks, cutting down the junk food and slowly go on to exercises at home.  With goals setup at stages  and motivation you will learn to maintain these.  So start off and best of luck...