〜てならない

Meaning

Expresses an emotion or sensation that wells up naturally and cannot be suppressed. As in 「残念でならない」, attached to words of emotion, it states that the feeling is extremely strong.

Examples

合格の知らせを聞いて、うれしくてならない On hearing I passed, I couldn't help feeling overjoyed.
一人で待つ間、心配でならなかった While waiting alone, I couldn't help feeling terribly worried.