Hello Good Evening,
Please do not take lightly, this injury
might be a ligament or meniscus
injury of the knee joint.
You should aware that knee joint itself has some ligaments and meniscus for proper functioning, but in your case it seems that they are disrupted, because pain and tenderness has increased with difficulty in flexion and extension.
So please go to orthopedic surgeon for a X-ray Knee and after clinical examination Arthroscopy
may be needed for diagnostic and therapeutic purpose.
Dr. Naresh Jain.