I Have Pain Discomfort Just Above My Buttocks On The

I have pain discomfort just above my buttocks on the back right side when I walk or lay on my stomach too long. When I walk I also have discomfort in my upper legs like I'm straining it. I cannot walk long distance and not much of a short distance without needing to sit down for a while. I also cannot stand in one spot for any longer than a couple of minutes before needing to sit down. Help!