Protein powder while nursing?

I need some insight from my fellow work out mommies. I'm a FTM and I would like to take protein powder (specifically fit miss) eventually after my baby is born to help me tone up my muscles a bit, I know a concern would be getting enough calories, I would use it as a meal replacement but mainly for my muscles. But their is the concern that I have no idea if that stuff is ok, so has anyone else used it or planned on using it while nursing? And also what your concerns would be about it?