How to rotate a sprite after using LookAt in 3D

I have lots of bullets on screen, they're all sprites, and I use LookAt to face them towards the camera every now and then. For some bullets, like a knife, for example, I need to rotate them to point in the direction of their speed. I get the speed angle using Atan2, but I don't know how to make the sprite point towards that direction while also facing the camera.