Chronic disease most certainly causes depression and PTSD. It's not an easy thing to manage either. I've seen people just plain give up and choose to die rather than fight. Guess what happens, they literally do die because they don't fight to keep on going. You have to have hope to keep going, and a belief in something. Personally I do believe in God and an afterlife, finding hope might be hard otherwise.

I know you've been through a lot, and I'm glad you're pushing on ahead. Keep that faith alive!