Baby measuring behind

Okay ladies, I'm a first time mom and I'm currently 37 weeks and 3 days. I went to the doctor on 7-10-19 and found out baby boy is 5 lbs 6 oz and measuring 2 weeks behind. I go back on 7-15-19 to see if he's gaining weight if not their going to induce me. Should I be worried? I don't understand why would he be measuring behind.