What Causes Progressive Pain In Right Posterior Buttock And Upper Thigh?

Thank you, over the last week and a half I have experienced progressing pain in my right posterior buttock, upper thigh (where they meet). Now the pain is down to my mid-posterior thigh. I can't walk comfortably and using the right leg to go up stairs is extremely painful and I am not stable. It doesn't feel like the sciatica I have experienced in the past and I am not athletic so a pulled hamstring seems unlikely, but it is interfering with normal activities of living. It is painful at rest now too. I am on Meloxicam so haven't tried any other anti-immflamatory than Tylenol. It's driving me nuts what do you think this is and how should I treat it?