It sounds like you're doing a good job on your eating. I know a lot of women who don't loose weight breastfeeding, and I didn't loose as easily the 2nd time as I did the first. So, unfortunately it could just be the way it is, and try not to get discouraged.
I didn't exercise at all after my first, and lost it all in 6 months (45lbs). With my second (still 45lbs), I was running by 5 weeks and worked out 3-5x a week and still took me 6-8 months to loose it all!
Before you cut calories, I'd see about changing up your workouts. Maybe you need more cardio, or if you're not doing a lot of strength training, maybe you should add that. If nothing else, you'll feel proactive and have more energy. That way, even if you don't loose any weight until you're done nursing you'll FEEL better and have a great start on your routine when you ween.
It could be your thyroid, but you'd probably be really tired and lathargic too...and for your sake, I hope it's NOT your thyroid!
Patience and Fortitude - Mom
There ain't a thing I've faced that's been too much for me - Classified "Inner Ninja"