Hypothyroidism is a much more likely candidate to explore..that should be treated, and in addition, look to the possibility that you are still an emotional eater dealing with emotional issues that you should address directly rather than medicate.
It seems plausible but if it were due to the med I probably would have expected weight gain earlier. Prozac is also said to be one of the better drugs for minimal weight gain as a side-effect.
If it were me I would probably be discussing hypothyroidism with my doctor and also looking at the possibility of emotional eating. Emotional eating is something we sometimes do to manage our emotions. This can sometimes be done subconsciously.
If you feel emotional eating may apply you could check out Dr Gould's website (shrinkyourself.com).
Good luck!