クリスマスが終わったらまたダイエットをしなくてはならないみたい。

Christmas

indicates sentence subject (occasionally object); indicates possessive (esp. in literary expressions); but; however; still; and

to finish; to end; to close

again; and; also; still (doing something)

diet; losing weight by any method (e.g. exercise)

indicates direct object of action; indicates subject of causative expression; indicates an area traversed; indicates time (period) over which action takes place; indicates point of departure or separation of action; indicates object of desire, like, hate, etc.

to do; to cause to become; to make (into); to turn (into); to serve as; to act as; to work as; to wear (clothes, a facial expression, etc.); to judge as being; to view as being; to think of as; to treat as; to use as; to decide on; to choose; to be sensed (of a smell, noise, etc.); to be (in a state, condition, etc.); to be worth; to cost; to pass (of time); to elapse; verbalizing suffix (applies to nouns noted in this dictionary with the part of speech "vs"); creates a humble verb (after a noun prefixed with "o" or "go"); to be just about to; to be just starting to; to try to; to attempt to

if ... then; when; and; why don't you...?; the more (one does something); because; since

-like; sort of; similar to; resembling