I totally understand you. I meet the same situation in game dev from time to time. There are weeks (or months) which are extremely productive but also weeks (and also months) where I get distracted by basically everything. And beeing a passionate gamer doesn't make it easier ;)

My advice is actually to work on your hobbies (writing or whatever) only if you are in the mood for it. Usually, the results are better when you enjoy the time working rather than forcing yourself into it.