I am very sorry to hear that your knee is injured and I strongly recommend that you to see a doctor to make sure whether it isn't serious.

In my opinion, as long as the bone of your knee is not injured, everything will be okay.

You could also delete "of your knee," since it's implied that you're talking about the knee.

For people atof our age, the most important thing is health.

If we have healthy bodies, we have everything.

More natural: "Health is everything."

I hope you will recover soon and wish you all the best.

Last winter, my left shoulder had a severe pain and II had severe pain in my left shoulder, and it often woke me up two or three times at night because of the pain.

I went to the hospital and had somea treatment done.

Or "underwent a treatment."

Later on, a colleague recommended me tothat I see a private doctor, and he gave me some plaster and Chinese medicine.

Unclear who "he" refers to in "he gave me."
If he = the doctor, I would write: "Later on, a colleague recommended that I see a private doctor, who he gave me some plaster and Chinese medicine."

After taking those things, my left shoulder could finally rise upI could finally move my left shoulder, though itI was still hasin some pain.

Another saying is that the pain and limited movement of shoulderI've also heard that/People also say that shoulder pain and stiffness will get better when the weather gets warm.

A saying is a specific phrase or proverb. Limited movement of shoulders = "stiffness"

Anyway, I hope you are curedfeel better soon.

Other standard variations: "I hope you get well soon," "get well soon," "feel better soon," "I hope you feel better soon."