Measuring small

Had a doctor's appointment on Thursday and I measured 36 weeks. The week before that I was measuring 37 weeks so it has me confused. I'm currently 38 weeks exactly. The doctor had me do a NST last Thursday after my appointment. Then yesterday I had an ultrasound done. I was measuring at 35 weeks and 6 days and I was 37 weeks and 6 days. My baby boy is 5lbs 15oz which they said is smaller. And he is low on percentiles. Did anyone else have this issue? If so, we're there complications with delivery, the baby, or health issues afterwards? I'm so worried about this now. I only have 2 weeks left and am trying not to stress and enjoy the last bit of this pregnancy but my mind is racing with worry.