On my way to the ER at 37+4 due to decreased movement

The baby is messing small, at 37 weeks he was only 5lbs even though everything seems to be normal. They don't seem to know why or if there is a fetal growth restriction. Had an NST yesterday and it was good. But today he doesn't move as he used to, very sluggish and much less movement. So my doctor told me to come in for another NST and go from there. I'm really scared and worried :/