Megan Fox I'm Already Skinny After Just Having a Baby

3/22/2014 11:47 AM PDT
Don't expect Megan Fox to wear mom jeans after popping out another kid last month ... because she already lost all the baby weight -- in 5 freaking weeks! 

Fox ran some errands Friday in Los Angeles with her other son Noah -- after giving birth to Bodhi Ransom in February -- and one thing is clear, girl was looking GOOD.

Congrats ... to the dads in her "Mommy and Me" classes.