Hi Jemsath,
Don’t worry. It could be some bugs in iOS that affected the performance of battery. Do try “Settings – General – Reset – Reset All Settings” and that mostly helps fixing such iOS related issues.
Monitor for 2 days and see how it goes. Depending on the apps usage the battery consumption differs though.
Make sure to update all the apps to latest version. If you are seeing no difference in battery performance after all settings reset, then the last option is to do iOS Restore by connecting your iPhone with computer and launching iTunes. You can find tutorials in youtube normally if you have any doubt with that. Also very important thing is taking backup before doing any such restore as it will wipe off the phone data completely.