Seroquel is a great sleep drug if you're really suffering from insomnia and the resultant sleep deprivation is making your mental health much worse. But I recommend it only as a temporary solution. Also, I would avoid extended release Seroquel XR unless you have a very fast metabolism, because for many people it creates a state of unbelievable grogginess for up to 16 hours after taking it. Plus it takes 3-4 hours to kick in at night. It's just a shitty drug. The IR formulation is okay though.
Before recommending Seroquel though, I suggest just switching your Xanax for a benzo that works better (as suggested by most of the posters above) and adding Melatonin to your combination. Melatonin works great for many people and it extends your sleep cycle.
Also, for long-term improvement in the quality of your sleep, I suggest practicing yogic breathing and doing gentle, nighttime yoga routines (no stimulating poses. You can find suggestions for sleep-enhancing routines on the internet.) And intense exercise early in the morning will help improve the quality of your sleep over time as well. These are changes that take effect over a period of months.
I have had a weird relationship with sleep and insomnia for many, many years and I've taken a lot of meds for it. What works best for me is .5mg Xanax at night, 9-12mg Melatonin, chamomile tea, pranayama (yogic breathing), yoga before bed and intense exercise in the morning with gentle exercise in the evening.
But my current regime is the result of almost 2 years of gradual cessation of years of taking a combination of heavy-duty sleep medications (Seroquel every night for 3 years for one). So do what you need to do for now and keep in mind that when your mental health improves or you're not facing as many challenges, you can taper off the meds you need now. Sure, it's not easy. But basically, when you're ready emotionally and mentally, half the battle is already won and you just have to act on your intentions.