I Am A 61 Year Old Woman. I Run 8-10

I am a 61 year old woman. I run 8-10 miles every other day and am in good health. Only take a low dosage of levothroxin. No other medications on a regular basis. Lately, I have discovered a large knot on the back part of my knee where it bends. It gets worse after a run. I'm wondering what it could be.
Also, I experience some lower back pain lately after a run. I take osteobiflex and it does seem help. I was wondering if a teeter hangup or some other type of inversion might help my lower back. Thanks