How To Treat Knee Pain After Being Injured?

Hello, I am a 50-yr. old woman who injured my knee last weekend while raking moss in my yard. I didn't feel my knee hurt right away, but the next couple days I found it difficult to walk, and I can't straighten my leg without severe pain. I have had issues with this knee before in the past, with this same sensation that it will either buckle or go backwards, similar to a flamingo! I am debating on whether to go ahead with MRI or wait a couple weeks to see if pain goes away. What is your advice?