Okay, I've read through this thread and I'm going to throw in my thoughts here.
The amount of physical pain you're suffering from may not be all in your head. Getting checked out by your doctor as others have suggested is a good idea.
You also seem to have a very self-defeating attitude. I hope talks with a counselor or psychologist can help you, but you have to bring out some willpower yourself. Wanting to make changes in your life and actually working to make those changes are two entirely different things.
The things you've said about your diet are somewhat disturbing to me. I would highly suggest talking to a nutritionist. If you're not fueling your body properly it can cause a lot of problems, especially if you are at risk for diabetes or have some type of thyroid problem. Don't try to do too many things at once, concentrate on getting a healthy diet going. You may have to force yourself to eat a little if you're suffering from depression that kills your appetite. I would also suggest eating several smaller meals a day (5-6) rather than 1-3 large meals. This can be as little as eating a banana or an apple throughout the day (or some other healthy snack). Slowly develop a routine and try not to beat yourself up if you slip off the routine. Accept if you went off of it, try to figure out what caused you to break from the routine, and try to pick back up on it again. Losing weight from getting sick or simply not eating may make the numbers on the scale go down, but it is most definitely NOT good for the body to do it that way. True weight loss and exercise takes time. Don't buy into this crap they throw in magazines about 4-6 week programs. It make work for some, but for most, its a load of BS. In the real world, it can takes months (and sometimes a couple of years) at the least to make significant changes.
How much activity do you get per day? I mean just doing chores around the house and whatnot. Do you spend massive amounts of time just sitting around and/or laying in bed? If so, you could actually be suffering from Muscular Atrophy. Its more than being out of shape, the muscles actually deteriorate from lack of use. You have to start very small to build yourself back up if this is the case. Just because you're not feeling the burn or pain doesn't mean you aren't helping your body. You could just start by walking around your home and doing some chores or something. Just little things to start getting your body moving.
In Summary:
1.) Get checked for physical conditions. Find out what can be done to work around them if there are any.
2.) Speak to someone about the mental aspects of what you are going through and come with mental exercises to get you over the hurdles.
3.) Rally your will. You CAN do this, if you really want to. If you don't, there's nobody that can help you if you're not willing to put forth your own effort.
4.) Begin implementing a dietary plan. Smaller meals and snacks more often during the day can stimulate the metabolism and help with calorie burn.
5.) Begin light exercises geared towards treating muscular atrophy.
6.) BABY STEPS! Don't push too hard, too fast. You don't have to break yourself to be healthier.
This is going to be my only post on this thread. My attempt to help even though I'm probably regurgitating what most others have said. Every post I've seen from the OP on this thread has been incredibly negative. It seems everybody here is willing to support you and offer advice, encouragement and assistance. That's a wonderful thing and very heartening, but you can't help somebody if they won't help themselves.
To the OP: You've got a lot of support here on this forum, but if you just sit around talking about how bad it is without trying to find a way to change things, no advice anybody here can offer will do you any good. Start letting go of that self-defeating attitude. It can be a hard change, especially if its something you've been doing for a long time, but it can be done. And its going to be the 1st step towards succeeding in what you're trying to accomplish here. Good luck to you. You can figure this out, if you want it bad enough.
