As you get older your metabolism slows down. As you put on weight your metabolism slows down. As you get older you lose muscle mass, which slows your metabolism down. And usually our jobs are more sedentary, so our metabolism slows down. You have to watch your diet, become more active, and do some type of muscle building exercises to try and bring your metabolism back up to decent levels. You might also want to have your testosterone levels checked.

See a nutritionist if you can. Get on a good diet and start a good exercise program, with some cross training. Just like always, it's a lot of work, but worth it in the end. Just remember your joints now have more pressure on them from the extra weight, so don't go out and do too much at the start as the pounding on your joints can lead to other much more serious problems (and this includes your spine being pushed down harder too, which can lead to blown disks.).