My brindle bitch had this around the same age. I was hammering good food into her. Loads of chicken, beef, rabbit, tripe, yoghurt, fish, quality biscuit, pasta, bread, cod liver oil.
She was just growing too fast for her legs.
I put her on real cheap low protein biscuit for about 2 weeks and it sorted her right out. Then I got her back onto the raw but increased the bread and pasta so lowered the protein.