alternative sentence construction

Hello there Lorna -

Your second alternative needs a 'que' > making it: "después de que habías ido". [Or instead of the pluperfect you could have used the straight preterite/indefinido: "después de que fuiste", or "después de que te fuiste"].

See Kwiziq lesson > Using antes de que/después de que with indicative or subjunctive in Spanish (subordinate time clauses) (Spain)

If the subject is the same in both parts of the sentence, then the simpler construction is preferred - i.e., using just the infinitive [as in your first alternative].

An example containing different subjects, would be: "Después de que habías ido, María llegó" = "After you had left, María arrived".