。
Fred was at his wit's end from his wife's constant nagging.
Literal
Wife [possessive-の] naggingly scolding [to-に] Fred [topic-は] greatly-troubled [possessive-の] state [copula-was-であった].
がみがみ is a mimetic for persistent, grating nagging or scolding — the repeated がみ captures the droning quality. 大弱りの体であった is a literary construction: 大弱り 'greatly troubled' + の体 'the appearance/state of' + であった (formal past copula). This literary register applied to a domestic complaint creates a mildly comic formality.