35+3 and thinking I'm in labour.

I'm 35+3 today and I had my weekly ultrasound today. I had 5 contractions during my ultrasound and when I talked to the doctor, I also told him about my back pain and cramping so he sent me to labour and delivery to monitor me. When he came and checked me, he counted my contractions and they are 7-8 minutes apart. He checked me and I'm 2cm dialated. Yet, he thinks it's nothing to worry about but wants to monitor me longer. Anyone else been in my situation and went into labour later that night?