I can't really give advice on if it's slow but I've been growing autos, once they were massive I used a super soil then, I changed to Coco, didn't wash and rinse properly, this stunted my autos unbelievably so much I eventually had to pull them, then I over watered one, this stunted its growth, so what I'm saying is if you have stressed the plant by whatever means it will grow slow, is the light okay, are the temps okay, what's the watering like etc.