There are two issues to consider: happiness and productivity. As long as your lack of happiness isn’t causing you, over short-term or long-term, to not be a good Oveid Hashem then you can take your time working on happiness. Not everyone is meant to be bubbly all the time. If that is not the proper way for you to function and work properly then trying to do that will only hurt your productiveness. And of course, if you can identify what is holding you back then you can find a way to deal with it. Personally, I would never identify myself as a “happy” person. I had a rough childhood and recent events have caused me serious troubles. But I can function and be productive without being happy, and maybe some day I’ll figure out how to be happy too. If not being happy hurts how you serve Hashem then you have to try and fix it immediately though.
