Re: How much do you write?

Varies.  Some days, none.  Others, thousands.  What actually makes it to the publish button is often far, far less than is written.  And, often, much of the written is crap.

Crap as in, stuff that does not flow, entertain, or move the story along.  Worldbuilding geekery, character bios, stuff for future stories in universe, stuff for other stories in different ones.  And the stuff that makes the cut could still use polishing  A pretty good day used to be around 5k-10k.  Nowadays, it is much slower.  Haven't written like this in years, and it is a skill that takes some practice.

Re: How much do you write?

When I first started my series, I couldn't stop writing. I don't have any kind of life to speak of, so as soon as I woke up till I went to bed I was writing and it was coming out easily and fluidly. I think it's safe to say I got 6k words in each day easily, with some days reaching well beyond that(It was this addictive writing that actually got me to quit smoking, so more than one good thing came out of it). 

Book 2 went just as smoothly, though there were quite a bit more interruptions. Book 3 I had slowed way down, but I had read somewhere that it's good to stay in the habit of getting something down each day, even if it was only a paragraph or two. Books 1 & 2 only took me a couple weeks to finish, but Book 3 took about a month. Book 4...we won't even go there, lol 

I don't think burnout is so much a cause as much as having a comfortable space to write, not being in pain while trying to do it I'm sure would help a lot. Staying/keeping focused is also a major problem for me, as I'll start to think of other things I can or need to do. Even through all that though, I'll still try to at least get 500 words down in the story itself, not just the notes that take place around it