てしょうがない is a casual, spoken expression used to emphasize that a feeling or state is so strong that it cannot be controlled. It can be translated as 'unbearably (A)' or 'can't help but feel (A)'. This phrase comes from a more formal noun, 仕様(しよう), which means 'method' or 'way'; しょう is just an easier-to-pronounce version of しよう. The literal meaning is close to 'it is (A), and there is no way to stop it', highlighting that the state is so extreme it cannot be ignored or controlled.

This grammar pattern connects to the て-form of verbs and い-Adjectives, or the で-form of な-Adjectives.

• 新(あたら)しい子犬(こいぬ)に会(あ)いたくてしょうがない。
  I'm dying to meet my new puppy.
• 頭(あたま)が痛(いた)くてしょうがない。
  My head is unbearably painful.
• テストの結果(けっか)が心配(しんぱい)でしょうがない。
  I'm so incredibly worried about the test results.

A similar phrase, 仕方(しかた)がない, can also be used. The difference between the two is minimal, as 仕方(しかた) also means 'method' or 'way'. However, 仕方(しかた)がない is often considered a little more formal and is more likely to appear in written contexts.

• このドラマの続(つづ)きが知(し)りたくて仕方(しかた)がない。
  I'm dying to know what happens next in this drama.
• うちの子(こ)がかわいくて仕方(しかた)がなかった。
  My child was just so unbelievably cute.
• 暇(ひま)で仕方(しかた)がないから、散歩(さんぽ)にでも行(い)こうかな。
  I'm so incredibly bored, maybe I'll go for a walk or something.