Sometimes, you don't have to do anything.  Cold and damp weather are my knees worst enemies.  The lemongrass eo is a good remedy. I was diagnosed with Osteoarthritis last summer, and now I know why my knees will swell and be painful for no reason.  You may want to check with an Ortheopedic to find out exactly what your issue is.

I also found these wonderful patches from a company called "Naturopatch of Vermont" last year.  They are made with olive oil, arnica, cayenne, rosemary, lemongrass and ginger essential oils.  Their phone is 800-340-9083 and website is www.naturopatch.com

Or, you could attempt your own mixture of these wonderful oils and you will see how wonderful it works to minimize the pain and the swelling.  Not just on your knees, but most parts of the body these will work on.

Good luck.