动辄, 屡屡, 频频 — at the drop of a hat

規則 动辄 = at the slightest thing — DISAPPROVING of a needless repetition: 他动辄发脾气。
动辄 also attaches to a large number to call it excessive: 动辄上万元。
屡屡 = repeatedly — counting occasions, not necessarily critical: 他屡屡获奖。
频频 = again and again in quick succession — stressing FREQUENCY: 他频频点头。
All three are written adverbs, after the subject and before the verb.