Preterm Labor?

I am 30 weeks and some days and last night I was having what I assume is contractions. It was stabbing pain and tightening of my uterus. Also had terrible cramping in my lower back. Called the doctor and they said to drink two glasses of water, take Tylenol, and lie down. I did and after an hour it went away. All the while my baby was moving. I just woke up and got dressed when I realized my bump seems much lower. Should I be worried about going into preterm labor? Does my bump being lower mean that he has dropped?