That's literally how my lower back feels. Like there's a burning sensation and I can feel muscles tightening I just assumed they were Braxton hicks. This has been going on for a few hours now. It started about halfway through my work day and now I'm home and tried laying and sitting, neither helped. The pain is tolerable but still hurts. I've tried stretching and cracking my back and that hasn't helped either. I have no idea what contractions feel like since this is my first baby but This doesn't feel normal. The pain kind of radiates through my tailbone. I thought it could be the sciatica nerve but it intensifies every so often and I've literally never felt this.