Thanks for all the replies, y'all. I'm still staying very productive, and it's Spring Break for me. I'm averaging three to four hours of productive writing time, and I'm a good half of the way through my novel's third draft in the month of March. I'm going to try to get through the last half in April.
I'm editing hard right now, and find that I can work about 1 hr straight and then I need to get up and move around. But by working an hour at a time, for three to four hours, I can get a good bit of writing done without being too tapped out by the end of the day.