I'll be honest with you. The longest period that I have consistently kept a journal was one year. I was at the worst of my depression and one of the things my therapist assigned me was to come up with five things I was grateful for every day, and her rule was that I couldn't come up with a list and re-use it, I have to have five DIFFERENT things from the previous day. She would check the journal, so I really felt like I had to make the effort.

But once I got into the habit of being grateful, I no longer needed to write every day, so now it's random.

I'm also not the type that thinks journaling is something you must do on a daily basis, but I've found that if my mind is swimming with thoughts, putting them down on paper forces them to line up in an orderly manner so I can get them down, and it really helps me clear my thoughts and notice connections I wasn't able to notice in the clutter.

tl;dr whatever works for you is what you should do! *hugs*