@SarahGen-- Absolutely, knee nerve damage can lead to all of these.
Weakening of muscles is highly likely when the femoral nerve is damaged. This is a major nerve in the leg. When it's damaged, it won't interact with muscles as it should and the muscles in turn stop working. When muscles are not used, they weaken and this may give legs a thinner appearance. For example, the Guillain-Barré Syndrome is a condition where muscles stop working and become weak due to nerve damage.
But there is no way you can diagnose the cause of your symptoms on your own. Weak muscles can cause knee pain and swelling too. It doesn't have to be nerve damage. Getting an MRI and an evaluation by a doctor is the best way to figure out the cause.