WordNet records no synonym and no antonym for growing pains. It is the only member of each of its synsets, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
pain in muscles or joints sometimes experienced by children and often attributed to rapid growth
emotional distress arising during adolescence
problems that arise in enlarging an enterprise (especially in the early stages)
Synonyms, antonyms and the broader and narrower relations for growing pains come from Princeton University’s WordNet. Full sources and licences.