I made a cake, but it didn't taste good. What did I do wrong?!?
Just teasing you, but that's how hard it is to say what happened without any information at all.
In your case, it could be the recipe. It could be the yeast strain. It could be the ingredients. It could be that fermentation wasn't finished. It could be that the priming sugar isn't finished. It could be that it isn't fully carbed up yet.
So, no one can say at this point. But if you post your recipe, and your steps, and any hydrometer readings, we can figure out what went wrong and how to fix it for next time!