Keep pushing. Do what makes you happy. I know it’s an ongoing battle, but feeling that happiness even for a split second makes it worth while.

You don't have to do anything but sit. I'm not joking. What did the Buddha do? Sit.

Heh! That's a really good one and true. But if I sit too much longer, I am going to be sitting underneath a tree and homeless.

I know its a struggle and harder to do than say. Take things one day at a time. Focus on making it through your day and improve on yourself in one little way each day. Like racheal said keep pushing. That's all you can do. When life gets you down just remember youre really important. People care about you. Never forget that <3

I don't know what I am going to do with the rest of my life.
What are you going to do today? Just today. It sounds corny but listen to your heart. Your heart will tell you what to do.

I've been on disability for the past 4 years and I am struggling mightily to get off of it.
Why struggle to get off it? Social security is a good way not to have to worry about money, I would think; at least, until you definitely have an alternative source of income.

It seems like each opportunity I manage to fail and find myself back to where I started or even below that point.
What did Edison say about the invention of the lightbulb? Could fail a 1000 times but only needed to succeed once. Easy for me to say: you're the one who never has to give up, no matter what!

So now I am trying to get back to work again but what is the point when I can't do anything?
I'm sure you can do something. You say 'work again' which means you have some experience in the working world which should serve you in good stead.

Sitting under the tree would appeal to me: the Buddha did just that prior to his enlightenment! The Bodhi Tree was a large and very old sacred fig tree located in Bodh Gaya, under which Siddhartha Gautama, the spiritual teacher who later became known as the Buddha, is said to have attained enlightenment.

I should be happy because I got weight loss surgery and I am down 48 pounds total in just over a month.
If you were brave enough for that surgery you can do anything, in my opinion.

Some times when I'm feeling a bit hopeless or not confident in myself, I like to remember this scripture at Isaiah 41:10 that reminds me I'm not alone. Even though I may lack trust in myself, I trust God and his ability to help me and be with me during tough times.