Not a stupid problem! Knee pain can be debilitating!
Have you seen a doctor? You need to make sure there is nothing serious going on before taking advice from us here, even though some of us do have experience with knee issues...
If there are actually parts of your knee rubbing together, it is a problem...a problem that can be treated or, at least, helped by physical therapy.
For now, for exercise, do the best that you can. Do whatever activities you can manage, and as frustrating as it might be, stop if it hurts.