I tried an SSRI once because my GP thought it might help keep the IBS calm, and I only took one 10 mg pill once and got really bad side effects (everything from throwing up and feeling incredibly nervous to getting blood in the urine) and I wasn't myself again for days. So I don't ever want to try that again. Happy for you though that you haven't had any side effects from your medicine.
For antidepressants it's pretty typical that you get side effects the first few weeks and then they get less severe or disappear. It could be that your bowels getting slower was a "side effect" from the medicine... But I don't want to take away your hope completely. Why not give it a while longer? You don't have anything to lose by doing that right? And remember - even if the effect wears off on some people it doesn't mean it will for you. I have freaked out when people have said time and time again on these boards that Imodium only works for a while, but I've been on a generic for 1.5 years and so far so good. And I am sure hoping it will continue to work. And I know a woman who has taken the same generic for years and it still works for her so...
By the way, how did the hernia thing go? Not sure you've read the post I wrote the other day but it looks like I will get a colostomy. But I am really happy about that.