Boot into safe mode. That will run the phone but without any apps you installed. If that works, you can back up all the apps you installed (you can back them up, they just can't run). Then delete them all. Restart (you'll boot into normal mode) and add the apps back, one by one, restarting after you add each one, until the problem starts. That's the one causing the problem. (Boot into safe mode, uninstall that app, restart and reinstall all the others.)
If even that doesn't help, it's possible that, if you updated over the air, you got a bad update. Go to your carrier (after backing up all your apps and all your data) and ask them if they can reflash the phone. They'll know, a minute after they reboot after the flash, whether there's a problem or not. (Some phones, for whatever reason, have to be flashed a few times before it works.) You'll probably lose all the apps you've installed, and all your data (because they'll do a factory reset), but you've got everything backed up.