I have severe osteoarthritis in both of my knees so I can relate! The pain does get worse when it rains, going up and down stairs and if I have to stand or kneel. It's unbearable sometimes. I have tried all of the over the counter medications to help and the only one that came close was Aleve. Although, it does make me a little sleepy, so I only take it at night.
Luckily, I went to my physician and told him I could not sleep sometimes because of the pain and he prescribed me something stronger. I would recommend talking to a doctor. They may give you something to help you which is stronger.