Can't get excited in daily Routine life.

I am happily married for last 2 years. I don't feel like having sex. I love my wife so much; but I neither have any affair outside or just don't get the excitement from her. She doesn't do any foreplay. She expects me to start the game. Even if I start it; I don't get excited and so can't have any fun even if I want to. My wife is little bit healthy; that could be the problem for my excitement or may be my job stress. I used to have a very good sex life. Now don't know what to do. Am afraid of my wife's feelings/ need left not taken care of. What to do..!! Should I take any sort of medicine..! I get excited these days only after watching porn. But neither my wife or I want that. It should be natural na. Thanks.