This is the 9703rd most frequent Japanese word.
苦しん
"苦しん" means "suffering" or "in pain."
苦しんでいた is used to describe someone experiencing mental or physical suffering.
彼は夜も眠れないほど苦しんでいた。
He was suffering so much that he couldn't sleep at night.
苦しんでいます indicates striving or struggling to accomplish something, implying effort and challenge.
子供たちは難しい問題を解くことに苦しんでいます。
The children are struggling to solve the difficult problem.
苦しんでいた expresses emotional pain or distress related to an event or result.