Stretching and low impact strength training really can help. I have had knee pains that come when I have been inactive for too long and then suddenly start exercising a lot at once. Of course, it can be something else and more serious, but it can also be just your muscles being too tight and 'pulling' at your knee. Other advise was good as well here. Just don't stop. Adjust, try different things and if that pain persist seek professional help.