I’m concerned that you didn’t mention a complete medical work up. The insomnia is a symptom. It is not a disease. You are not sleeping because something is very wrong. Yes, it might be depression. But it’s also likely that a medical condition is a contributing factor. Please, if you haven’t already, make an appointment with your doctor and ask for a complete battery of tests. Request referrals to an endocrinologist and neurologist as well.
If you are physically fine, then ask for a sleep study. One possible explanation for your lack of sleep is sleep apnea. That is a treatable condition.
The medications you are taking could possibly be making the situation worse. Do ask you doctor if you could be experiencing a rebound effect from withdrawing the ambien. Also ask about side effects of the other medications. A side effect of both Restoril and Seroquel, for example, is daytime drowsiness or tiredness.
Please don’t give up on finding an answer and finding a cure. You need to be an active member of your treatment team. Insist on getting the tests and support you need to get to the bottom of this.
I wish you well.