39 weeks pregnant bloody discharge and back pain when should i go to labor and delivery?

Now is good: You may have mucous show which is normal. However, if you have no fetal movements, or frank bleeding, or severe constant back pain; you should go straight to labor & delivery. It's safer to get checked & ensure a healthy baby, see if labor has started, & see if everything's ok. L & d staff should be happy to reassure you & answer all your questions.