I pretty much have the same problem, although no one has ever had the guts to approach directly me about it. Be thankful that you're at least getting honest input.
I would advise you to change your eating habits. That's a safe enough place to start. Be adamant with yourself. Identify foods that are unhealthful for you, and avoid them. Identify foods that are healthful, and seek them out. It's more difficult if you have to go to some restaurant where all of the food is basically garbage, but I have a feeling this won't problem if your social life is suffering as much as you implied.
Junk food can and does wreak havok with your body, and not everyone has an advance warning of this in the form of Body Odor . You might be thankful for that.
I can't overstate the value of good exercise. Simply walking for a few miles everyday works like an antidepressant, gets the mental gears going, and increases your energy level.