First of all, install the most recent service pack for SQL 2016, which is SP3.
Next, yes, you should try add more memory. 16 GB is not a lot for SQL Server these days.
Most likely this is an issue with your workload. Since we don't know anything about it, we cannot say much. But usually, there is a dump of used memory in the SQL Server errorlog when this happens. You can use this to see where the memory is being spent.