40 weeks & 2 days pregnant. was 1 cm dilated weds., losing mucus plug today, a lot of lower back pain & cramping in pelvis. what does all this mean?

Getting close : This likely just means you are getting closer to the big day. This is what you are waiting for.

Delivery!: Sounds like labor is close by. Lower back pain is often a symptoms of the cervix dilating. Your doctor should have given you instructions on when to go to the hospital. If not, call the labor and delivery unit at the local hospital for advice.