postpartum joint pain

My LO is 7 week now and I still feel knee joint pain. I wonder is it that I lost muscle + weight gain during pregnancy causing knee joint to be weak. If so, should I start doing exercise like squats to strengthen my thigh/knee muscle to support my knee? I dont have other joint pain like wrist or ankle. If there is any mummy who are workout trainer, could you advise what kind of exercise to improve situation?