Well, if you compare the Doctor from the show (mlp) and to the one you've made you can also notice that the colour of his fur is also wrong. But I won't judge since I could never be able to draw something like this.
Actually, I didn't draw any of this. As you can see, I've credited everyone whose vectors I've used. About the Doctor, the design used comes from a background pony seen at the garden party in the season 2 episode "Sweet and Elite".