Low platelets count. Is it normal?

My baby boy is 5 days old and admitted in the hospital on the day 1 due to vomitings. The reports are normal now. Even blood culture report is negative. The platelets count is a big worry for us. It's coming down gradually from 90k, 60k, 30k to 27k today. Doctor is saying the Baby seems to be clinically. They have tried punching the baby with syringe and bleeding is normal. He is suggesting for the blood transfusion only if the count comes below 20k. They haven't started any specific treatment for the platelets. They are using antibiotics from Day 1 and had a plan to stop the same if the blood culture is normal. Even now, they are using the same antibiotics. Should the doctor conduct any further medical tests to diognize the root cause of the problem or start any other antibiotics. ? The doctor is not ready to discharge unless the count comes above 150k. Can it come back to that level without any treatment? Is it normal? Please suggest the thing we can do now.