What Causes Recurring Tender Spot Below The Knee?

I have a tender spot on the outside bottom part of my knee. It healed and now it's back. I also periodically have twinges in my knees particulary if I over due it climbing stairs without proper shoes. I have been going to the gym and doing a mild free and machine weights program. I am 57 5' 6 " 133 pounds generally in good shape