Kay,
It is not uncommon for patients to complain that their pain is worse at night. This is because there is nothing to distract you from the pain. During the day, you can keep your mind on other things, but at night it is just you and your discomfort.
By definition, arthritis is an inflammatory disorder of a joint. But, in recent times, it has become a wastebasket term for just about any pain in the spine or extremities.
There are many, many causes of pain in the knee and muscles. Unfortunately, with just the symptom of pain, it is not really enough information to pin down a cause.
If the discomfort is getting worse and has not responded to the usual home remedies, then you may want to have your knees evaluated by an orthopedic surgeon.
Good luck.