I Have Been Having Excruciating Pain That Feels Like It

I have been having excruciating pain that feels like it is coming from my butt for about 4 hours now. The left lower back feels like it is burning and for a while the pain was going down into my left leg. It is lessened a bit now after laying perfectly still but there is still quite a pain. Do I wait it out or try to go to an ER? I have not had any nausea or vomiting.