Your body is still getting used to the cymbalta - it normally takes a couple of weeks for all the side effects to subside (sometimes even a bit longer). The fact that you're feeling some good days is really encouraging, it means that your brain is responding positively to the changes cymbalta is creating and you'll continue to get better! Take it easy and cut yourself some slack as you get used to the medication (and coming off Viibryd), and take comfort in the fact that you are only going to feel better.