I also believe it must be Prozac, it being an SSRI, and sexual dysfunction is kind of common on those drugs. I experienced that back when I was taking Zoloft (also an SSRI) where arousal took a while and it was much more difficult to climax (sorry for the TMI).

Oh, and yes, once I was on Wellbutrin with the Zoloft to wipe out the sexual dysfunction side effects from Zoloft, and luckily, it did work. But then I had to discontinue Zoloft/Wellbutrin for it inducing mania- even with my mood stabilizers in place. This often isn't an issue with people though, but if you are Bipolar Type 1 or have a history of full-blown mania, just be aware if you notice any warning signs.