I fell on my knee a month ago and it still really hurts, it is still bruised and i have a huge knot. could this be a contusion, or something else?

Hematoma or effusion: If you have a focal area of swelling, it could be a hematoma - collection of blood under skin. If swelling is more diffuse, you may have an effusion - collection of fluid inside joint. Given the duration of your symptoms, I recommend that you get it evaluated for possible aspiration (drainage). In the meantime, try ice and ibuprofen or naprosyn (naproxen). Take Care!

Yes: sometimes a large bruise can take a while to resolve and larger bruises with more blood collection or hematoma can become firm before resolving If you still have significant pain along with the bruise and swelling a month after the injury you may also need to be evaluated to rule out other injury or kneecap fracture