Mama, please contact your OB or go to the hospital right away para ma-check, 39 weeks na kayo, kaya better safe than sorry! Back pain na sobrang sakit at walang discharge could be many things, pero kailangan ng doctor to properly assess kung true labor na o something else.
One of my mum friends had similar experience at hindi naman labor, pero the peace of mind na na-check agad ay sobrang worth it, lalo na first time mom ka pa. Wag mag-antay, go na! Sending you all the best, and fingers crossed na healthy delivery agad!