How much do you weigh? I use light weight on squats due to a back injury and bone disease, but I feel like it's got to get done either way. You might need to start a 5x5 routine to get stronger and be able to up the weight. Heck, start by doing 3x5s for a few weeks and work up to the 5x5. It really does work wonders for busting through plateaus and when the weights just seem to "stick".