I love doing squats but, for about a year and half, i have not been able to perform this exercise because my left knee hurts. Each time I try to squat, there's a clicking sound in my left knee and, it hurts bad. As a result, even when I try, my right leg carries all the weight and, i don't feel the impact of the exercise on my quads. What can i do to remedy this situation or, how can i train my quads without squats?