I started a small dose of Wellbutrin (not SR or XL) a week ago and the only unpleasant side effect I have is constipation (with upper GI discomfort). The problem is, I already have moderate-to-severe constipation-predominant irritable bowel syndrome (IBS-C) and must take a prescription medication from Europe to manage it (Resolor/prucalopride). No other treatment or Rx helps my IBS-C. Even with the Resolor, it doesn't help the constipation from Wellbutrin very much. I added Miralax and fiber each day but since the problem is caused by reduced peristaltic waves and not diet or dehydration, those modifications don't treat the issue.
I've seen mixed responses as to whether this is a side effect that will likely go away over time or not. I also have fibromyalgia and want to stay on Wellbutrin if it will help my physical and mental energy levels in addition to depression. If the constipation doesn't go away, I might look into vilazodone/Viibryd.