Not a pulled muscle or anything. I'm scared symptoms I have are knee cancer, osteosarcoma. Should I see a doctor?

Yes. Grit your teeth and to it without delay. To be brave, act brave. Until you find you, you won't have peace.
Please see doctor. Please see your doctor for a complete history and physical. Further evaluation will depend on the findings of that examination, but may include radiographs, an MRI or even an orthopedic surgeon consult. Until you see your doctor, you will never know and just keep on worrying.