How does god determine who gets a good life and who doesn't?

I'm not religious, but I believe in the idea of god. I have been looking for answers for years and years as to why I have suffered such great pain in my life. I have prayed all I can, it's simply not working for me. I have done nothing BAD to deserve the life I have been dealt. The fact that the only advice i'm ever given is that I need to try and make changes, tells me that i have been put in a lose lose situation. I can only live the best I know how and if that's not enough then, there's nothing more I can do. I understand that everyone has experienced problems in their lives, but there's a huge difference between problems and down times and outright pain and suffering. I don't have problems, my entire life is all unfortunate cirstances. All I can do is pray and hope my demise is soon, even if it means suffering before I go. Does anyone know HOW god chooses our cirstances, because it's silly to say we choose our own cirstances when I don't know who i'm gonna meet tomorrow that may change my life or what catastrophe may strike tonight. I also didn't choose the childhood and adolescence i experienced that caused me to become damaged for life and mentally ill. Why do some have smooth lives while others have turmoil?