Hope it's ok if I answer. I've had this problem all my life and only in the last few years come upon solutions that worked.

The solution to consistency is to create what's called "tiny habits". If you want a complete run-down on how to do this, read Atomic Habits by James Clear or Tiny Habits by Bj Fogg (they are pretty similar in content). For the tl;dr version, watch this TED talk.

About a month ago, I decided to learn Chinese since I was taking a break from work and had some free time. I got to the point where I could read simple DuChinese stories, then 2 weeks in my motivation dried up. I no longer wanted to study for hours each day.

So, I made a tiny habit to read one page of a graded reader before bed. Just one page - it takes only a few minutes (the pages are very short). Some days, I read much more than that, but I never force myself to, because then I know I would quit the habit.

If you find you aren't doing your tiny habit every day, make sure your trigger is strong enough - e.g. "When I get into bed, I will read one page". Then practice doing the trigger followed by the habit to solidify it in your mind.

For more advanced habit making concepts, I really liked the book The Power of Habit by Charles Duhigg. It talks more about keystone habits, the role of faith/belief, etc.

Hope that helped. Happy habit making!