Exclusively Formula Fed diaper

My son is 5 days old, and I am an new mother.

Unfortunately I am not allowed to breast feed due to medication that I have to take - the medication can influence him negatively.... so we formula feed.

Today is day 2 back from the hospital. On the last day at the hospital, he had a poopy diaper at 3am and that was the last..... I am worried, but the nurse at the baby clinic said I shouldn't be..... but my friends say that I should?!

HELP PLEASE! This new mommy is panicky!