My Hip Or Side Of Top Of Leg Is Starting

My hip or side of top of leg is starting to hurt sometimes coming down the steps. I have 2 knee replacements that are a couple years old but no problem with them, The last week or so when I lay down in bed my left side and legs hurts. It's like I can't get in a comfortable position. I have to keep changing my leg position. I did have athritis in my knees. Once I am up I walk o.k.