Not seeing lower body gains


I want to gain mass in my chicken legs and little butt. After several months training with FB, I see huge gains in my arms and specially my upper back but not in my lower body and I'm starting to look a bit masculine and I don't like that.

The problem is that I never feel the burn in my butt. Never. My quads sometimes burn when I hold squats but my but never does. I lift all the weight I have at home for my deadlifts and bridges and nothing. I've tried doubling the reps. Nothing. I might get a sore lower back but never a sore butt.

I really don't want to buy more weights because my house is already cluttered enough (and the powerblocks price tag is out of the question). Is buying more weights my only hope?

PS: I have a knee injury and can't do anything jump-y.