Try step-ups. They are a modified lunge. This way you can work your gluteals without putting so much stress on your knee. Once you get better at the step-ups you can go back to the lunges and see if your pain has diminished. Lack of range of motion at the ankle, knee, and hip can also place stress to the knee when you lunge. Before doing your lunges, try foam rolling your calves, outside of your thigh (IT-band), front of your thigh (quadriceps), back of your thigh (hamstrings), and inside of your thigh (adductors). Foam rolling is a self-massage technique used to loosen the muscles that attach to the knee and help improve knee range of motion. Hold each tender spot for 30 seconds. Next, statically stretch your calves, the front of your thigh (quadriceps), the back of your thigh (hamstrings), and the inside of your thigh (adductors). Hold each stretch for 30 seconds. These stretches, along with the foam rolling exercises, will help improve the range of motion of your ankles and knee taking stress off the knee joint. Also, keep an eye on knee positioning when you lunge. Make sure that the front knee stays in line with your toes and it doesn't collapse inward or move forward past your toes. This inward knee position places a large amount of stress on the knee and can lead to pain.