Give it a couple days. After a major update there are often a lot of background tasks going on; rebuilding databases, downloading apps and data, etc. Make sure you restart it (power off). If it's still a problem after a couple days, you may have battery issues.
You can also check the Settings > Battery settings and see what apps, if any, are using a lot of battery. Pay close attention to those that may be operating in the background when they should not need to.