Painful, Agonizing
い adjective
This word ends in い, meaning you know it's probably an adjective. In fact, it ends in しい, which makes it even more likely it's an adjective. The kanji 苦 means suffering, so what could a related adjective be? This word means painful or agonizing.
くるしい
Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You didn't learn that reading with this kanji, so here's a mnemonic to help you: Everything is really painful right now. Why? You have something heavy on top of you, crushing (くる) you.
食べすぎて苦しい。
I ate so much that I'm in pain.
正直に言うと、一ヶ月前くらいから、このジーンズ、苦しいんだ。
To be honest, I've been struggling with these jeans for around a month now.
村では、冬になると食べ物が不足して、村人はみんな苦しい生活を送っていました。
In the village, there was not enough food in winter, and all the villagers lived in hardship.