My knee hurts badly! What can I do to alleviate the pain?

Knee pain. If you are having a lot of pain the first right thing to do is seek the help of a medical professional - in this case an orthopedist. As we don't know your medical history here, advising meds can be a bad idea as there could be interactions or allergies .
Ice. Ice your knee for 20 minutes at a time 4-5 times per day. If you can take an anti-inflammatory, over the counter, that would help as well.