Decreased platelets counts post 60 days stem cell transplant

My nephew who is suffering from ALL. He underwent 3 years of standard protocol but ALL relapsed after 3 years. Hence he went through stem cell transplant with father who was 50% match.

He had very minor GVHD on skin but apart from that no infection or GVHD till 70 days. Today doctor performed CBC report on Day 73 and found that all the counts are very low.

Hemoglobin : 9.0

WBC: 3500

I Platelets: 65000

Do we need to worry about it? Is it normal?

Really appreciate your responses. Thanks.