Start with walking for 30-40 minutes. I am not telling you to hop into weight lifting and give me 80 burpees tomorrow. NO. Brisk walking. If you have a park nearby, where people exercise, you can walk there and do some simple exercises. Or you can do Zumba at home, it you prefer to dance. Nothing extreme.
You need to drink plenty of water and eat well while you are on Duromine. It is a very potent medication. What dose are you on?
Don't eat huge meals. But eat often. have your sandwich for breakfast (wholegrain, no mayo, i hope). In 2 hours, have a handful of nuts or a tube of yogurt with berries. 3 hours later have a piece of grilled/steamed/boiled mit/fish/egg with a salad or stewed vegetables, 2 hours later have a couple of tbsp. of cottage cheese with a cucumber (half, a couple slices), 3 hours later have your dinner (something of foods suggested for lunch), 2 hours later have an egg/some cottage cheese/yogurt/etc.
Of course, it depends on how long your day is, when you wake up/have breakfast and go to bed, but the schedule is pretty like this.