being flu/cold cause blood cells to be low?

I was really sick with the flu, fever body ache, sinus,.. For 5days. My period was late because im sick. I went to the e.r because i felt sick n weak.. Like dehydrated.. They took blood test n said i looked fine, but my white cells n blood cells where a lil low.. Is it normal to be low because i was sick?? Im scared... He said maybe it can be that.. But to check in two weeks with my doc if my blood cells bust back up again. Is it possible that being sick cause this..??