Is it possible to still feel weary and tired after over a week of giving blood?

I gave blood a little over a week ago (1 pint), and when I try to go running like I usually do it's really hard for me to keep up with my normal pace or even run as far as I usually do. Could it be because I am small? I'm 5"3' and I think bout 124 pounds (I told them I was 126) and I am 16. I might actually weigh less than that but still I am pretty small. Could it be because of the red blood cells having to recount? Somebody please help. I haven't been able to workout like I usually do.