Hello and welcome
It seem that you have Iron deficiency
as your iron level is 39.
I want to know the Hemoglobin
level before you donate the blood?
Are you anemic or history of anemia?
What is your age and sex?
If you are anemic than it is quite possible that you can feel shortness of breath
and chest heaviness. Get yourself relaxed and take rest as much as you can. Keep yourself hydrated.
If you have not checked your hemoglobin level before than get it checked now and further decision can be made after that. Hope this will help you.