Pain after tibia nailing surgery.

I underwent a tibia nailing surgery on 26 August. My fibula was also fractured but doctor left it unattended attended. I am having physiotherapy sessions and conditions have improved a lot But since last 4-5 days I feel pain slightly below knee area. This pain mainly occurs when I bent and unbent my knee or when I raise a leg during exercise. This pain becomes less after exercise but gradually appears again when I bent knee or raise my leag after sometime. Please tell me if this is normal. Isn't there any issue with nail or healing? I am moving around with Walker and give partial weight on affected leg and also sit on sofa without putting my leg on any raised object. Need clear cut reply please. Please give answer as a help as it will relax me