Jae, I don't think you're doing enough reps. Even if you are just trying to strength train, a few sets at 6 reps is not enough exercise mang. When I had a trainer he told me 10-12 reps was where it's at for building muscle... if you can do more than 12, then it's time to increase the weight. After you've done a few of those, sure, go for your max... but if you just do the straight up heavy shit, I don't think you'll see much progress.