38weeks pregnant back pain milky discharge and tightenings am i in slow labour?

Quite possible, but: At 38 wks, labor can start any time, but the milky discharge is a bit concerning. Typically discharge during pregnancy should be relatively clear without odor or associated burning/pain etc...Loss of mucus-plug is likely your 'mikly discharge" or if you just had relation, milky discharge could just be semen. Please see doc for eval. Good luck to you.