Hip replacement: What are the symptoms of failure?

Hello, I had my left hip replaced in 2003 at the age of 60. Great results! However, I am wondering what the symptoms of failure might be? I have a lot of arthritis and had my left knee replaced in 2017 and am planning to schedule the right one after Christmas. Meantime I am walking with a bit of a limp. Sometimes I have pain in the area above the top of the femur (that sort of indentation before the buttocks connect. No groin pain. Hip surgeon told me he didn't know how long the hip would last.....probably more than 15 years.....I am now at 16 yrs. Also some nights I have trouble sleeping on the left side. Comments? Thanks! Pat