You might have a problem with your form on the DL if it causes you pain, in which case you would need more than 12 reps/week to reinforce good form... something like 8x3 with relatively light weight (start at say, 8-10RM) and ~1min rest periods (so that it doesn't take 30+ minutes to do all 8 sets), or even 4x10 if you can maintain good form for 10 reps. 5x5 would also work, if you start light enough that you can focus on the movement. Hell, 6x6 would give you an extra 22 reps/week over 5x5. For working on form, there are a lot of options, you just have to find the one that you're most comfortable with.
Of course, if you don't think its a form thing, disregard that advice. I would still do more than 3x2, though how much more really depends on your goals.
Also, ditch hamstring curls for something more useful.
Possible replacements for hamstring curls:
* bulgarian split squats (possibly too similar to lunges)
* Glute-ham raise (if you have the equipment)
* ghetto glute-ham raise (if you don't)
* reverse hyper (if you have the equipment)
* dumbbell or kettlebell swings
I would lean towards the latter four, and all of those I would personally do for higher reps, 4x8 or similar.