My whole knee is in pain. I'm 18 and I noticed a little bit of swelling at the end of the day. This has been going on for a couple weeks now. What to do?

Physical therapy. For a majority of knee pain, we start with physical therapy and NSAID's (I.e. Motrin, Aleve). If it persists with symptoms of effusion (swelling), instability (giving out), and/or mechanical symptoms (logging or getting stuck), then we may get an mri if the X-rays are negative. .