What Causes Sudden Pain In The Upper Hips And Legs?

I am having sudden onset of pain in my left upper hip & the pain lasts for a few days & then goes away. It does not radiate down my leg. There is no predicting when it will hit. I can just stand up & all of a sudden I am in a lot of pain or when I am doing yard work, whatever. It s so bad I have a very hard time walking. I don t know what it is or if there is anything I can do to keep it from happening (it is happening maybe every week or 2 lately). I m 63yrs. old with a history of hypothyroid & breast cancer (5 yrs. out). I m taking Synthroid & Letrrozole. Thanks so much for your help!