go after each other vs go at it

go after each other

go at it

verb
  • To engage in some activity, especially vigorously or enthusiastically. 

  • To have sex. 

  • To fight. 

  • As go at + it; spoken emphasis typically on 'go'. 

How often have the words go after each other and go at it occurred in a corpus of books? (source: Google Ngram Viewer )