it's totally fine....happened with my donor. She may have lots of follicles just soaking up the e2 and prepaing to explode into a great cycle. I frankly did not believe my nurses and I thought they were lying to spare my feelings when my donor got a slow start. She did retrieve late (day 17) but produced 27 eggs, 25 mature, 23 fert. She made 15 great blasts and I have a baby.
hang in there.