I would call--I had a bloody show when I woke up in the morning (39 weeks + 1 day), but didn't feel any labor-type feelings. Did my Googlin' and came to the conclusion that we would be having a baby within the next few days. I went ahead and called my doctor, who told me to come in for a quick check... yeah, she sent me straight to the hospital and my baby was born that afternoon. Apparently I was having contractions but didn't feel them.
At 38 weeks... call your doctor. What can it hurt?