That's one of the problems with these drugs. If you go off them, sometimes they don't help as well if you go back on them. I experienced this with Anafranil. Perhaps you just need to be on them a little longer this time for it to work, even if at a higher dose.

Fortunately, there are also other medications you can try, if Prozac doesn't work for you (enough) anymore. And you didn't mention side effects, but some drugs may have fewer side effects for you, if that's a problem.