Talk it over with someone qualified to give sound advice. Online advice is not the way to go with drugs.
First of all, I really doubt that the Prozac is still doing you any good. Our bodies build up a tolerance to these types of medications and we're lucky to get even several years out of them and no where near 15. I'm guessing it's your GP prescribing your medications when it should be a psychiatrist. I know of no reason you can't take these two medications together, but I would see a psychiatrist for treatment, they are the most knowledgeable when it comes to what medication is best for us. Why is your doctor wanting to add a second medication?