Hi aisyahaziz,
I understand you are experiencing performance issues on your device.
I would begin by ensuring you have a backup of your data.
There may be an issue with your battery. You can learn more about battery and performance here: iPhone Battery and Performance.
If your battery is in good condition, continue with the following.
First, Reset All Settings. You can learn how to do so here: Return iPhone settings to their defaults.
If you continue to have the issue, I recommend you Erase All Content & Settings. You can learn how to do so here: How to erase your iPhone, iPad, or iPod touch.
If the issue continues thereafter, I would encourage you to Contact Apple Support.
Hope this helps!
Thank you for using Apple Support Communities.
Cheers.