Wow, all of the prior posts have contained great advice!
I would add only this: you have identified that you've climbed 3/4 of the way up a ladder, only to realize it was placed against the wrong wall. Just guessing, I would say it would be hard to throw a rock around these parts and not hit someone who has had the same experience.
I had 3 years of law school and 10 years of practicing law before I finally left, and I totally agree with Ahimel's point that it did not get any easier to quit as time went by. Quite the opposite, actually. I knew in my first year of law school that that was not the place for me, but I kept gutting it out. Having done it, I feel like I made the best of the situation and certainly learned a lot, but I don't know that I would repeat the process, given the option . . .
So, I've got no words of wisdom about how to keep climbing the ladder (staying motivated, managing your time, etc), just a cautionary tale about how long that climb can go if you're not careful.
Good luck!