Hello! I Am A Very Active 63 Year Old Woman...run,

Hello! I am a very active 63 year old woman...run, walk bike etc. Sometimes my hip is stiff and the muscle is tight when I'm walking/running...once I get going, it almost feels like something shifts in my hip and the tightness or pain just goes away! I stretch after and it's fine, but then sometimes during the day I get the ache again in my hip...feels like a muscle to me..Thank you for your help (: