I think you need detailed clinical examination and imaging to come to a diagnosis.
It is too early to conclude that you have osteoarthritis of the knee.
There maybe extra articular causes of knee pain
which may be bothering you.
You should see a good orthopedic surgeon
who can diagnose your condition.
Meanwhile you can apply ice for 20 minutes every hourly for two or three days and then as in when you have pain
Tick rest when you have pain but a device keep your mobility on so that your joint will not become stiff.
I would suggest that cycling would be a very good exercise for you as you have both knee and back pain