prozac not working after years

I am not totally sure on that.. I took it off and on for about 3yrs.. The last time I took it, I ended up going off it again due to servere migraines. The first time I was on 40mg and that lasted for quite a some time(close to a year) then I was bumped up to 60mg. That helped with the depression but I became VERY shaky.. my hands were no longer steady and I began to feel weird. I was put back to the 40.. I ended up for a while being on 50 meaning I had to take a 40mg and a 10mg.. This last time I couldnt even tolorate the 20mg.. Prozac was no longer helping me at all.. I had heard through the grape vine so to speak that if you are on prozac and its working, stay on it cause once you go off it, it will never work for you again. I guess in a way, (for me) that was true cause it didn't work for me anymore. My mental health Dr said that it isn't true but who really know's?? I don't know if this answer's any questions or not but I am still in the process of trying to find the "Rught" anti-depressant medicine that will work for me without increased migraines (which I have chronic daily migraines). and something that will help out with my anxiety and panic disorder.