I have a dataset with sample size of 187. my dependent variable is depression at 3 different time points, a, b and c (continuous). My independent variables is a categorical sexual abuse vs those with no sexual abuse. I am interested in creating a nested design model which will account for the fact that I have data at three-time points (pregnancy, 6 weeks, and 12 weeks). What is a step by step process for performing the GEE analyses on STATA?