Should i be worried

Not sure if i should be concerned or not but am , at 33 weeks my bby was estimated weight at 3lbs 14oz . im now 37 almost 38 weeks ive only gained a pound in between time. .. Im now being moniter every week w ultrasounds n seeing the doctors i just had an ultrasounnd done yesterday n her heart rate was in the 150s when normally its always in the 160s and took her 10 mins to practice breathing .. My first daughter was 5lbs 10oz