Hi @meganlydia Just to clarify it is Fast charging you have an issue with and not Super Fast charging? Are you using a Samsung charger or an alternative? The fastest you would be able to charge wirelessly is 15 watt but there is a wired 25 watt Super Fast charger. If you are only fast charging could try ensuring that just Fast charging and Fast Wireless charging selected. Superfast Charging needs to be selected if using that option.
An idea to clean the charging port however as @LiquidSnake has suggested if still issues it is advisable to wipe the cache partition. This will delete temporary files but does not affect your Data.
Follow these steps: