Braxton Hicks?? 39weeks

So I’ve been getting Braxton Hicks constantly throughout this pregnancy, some painful, some not. I’m 39weeks pregnant. Today, constant new back pain with severe cramps in pelvis and tightening for the last hour and had loose bowel motion this am. This is definitely more painful than Braxton Hicks. My question, can constant severe back pain be a sign of labour or is it suppose to come in waves like contractions? Since the pain has started it hasn’t come in waves like contractions to even time them.