Your situation is common for many people with arthritis. Pain limits motion, which limits function. The less you move, the more it hurts. The more it hurts, the less you want to move. It can create a vicious cycle.
But it's also true that motion is lotion. And strengthening the muscles around the knee improves general joint stability. The more stable the knee, the more functional it will be.
The best way to approach this problem is by making changes slowly but steadily. First, talk to your doctor about getting better control of your pain so you can start exercising more. The careful use of the right medications can make all the difference.
Many people don't want to take drugs. Consider this a temporary solution until you can get back up on your feet, so-to-speak. Once you can progress in an exercise program, it may be possible to reduce and even stop taking pain relievers.
The right type and amount of exercise is also important. You may want to consult with a physical therapist to get you started. Once the therapist assesses your motion, strength, and stability, then an exercise program geared toward your needs can be prescribed.
You'll be able to do this on your own at home with occasional guidance from the therapist. If you find it difficult to motivate yourself to exercise, think about joining an exercise group. Your therapist will be able to help you find community resources for this type of program.