The noun suffering can be countable or uncountable. In more general, commonly used, contexts, the plural form will also be suffering. However, in more specific contexts, the plural form can also be sufferings e.g. in reference to various types of sufferings or a collection of sufferings.

Is it suffering or sufferings?

The word "suffering" can be used as an adjective and also as a noun. The noun "suffering" is used as a mass noun (i.e. uncountable noun). The noun "sufferings" is used as a countable noun in the countable sense.

Is hardship singular or plural?

When you're talking about hardship in general, as a concept, you use the singular. It's an uncountable noun. When it's modified, you can use the plural-- hardships of war implies many ongoing and different instances of hardship.