"In vain" and "for nothing" mean two separate things in English.
Crying in vain- the reason for crying may or may not be justified, but crying will not improve the situation.
Crying for nothing- the person has no reason to cry.
It's my understanding that „degeaba" means "in vain". To express "for nothing" I would think „pentru puțin" ori „fără motiv" would be better translations.