Working out too soon?

I'm 2 weeks PP and really wanting to get back to my daily work out routine. I've been doing some squats and push ups a little bit a day, but what I really wanna do is sit ups. I've been told doing sit ups too early after delivery and ruin your muscles in the long run. Has anyone started working out immediately after birth?? What are some more small work outs I can do until I can start getting back into my routine???