Maybe your exercise can be to direct your thoughts elsewhere. Start with 5 minutes instead of 30 and actively try to think about something else when your though

Maybe your exercise can be to direct your thoughts elsewhere. Start with 5 minutes instead of 30 and actively try to think about something else when your thoughts become too negative. I can't guarantee it will help you but it's a sort of meditation that's worked for me when I felt like my brain wouldn't turn off.