I would definetly drink lots and lots of fluids.
But yes, the effects of giving blood to depend on your size/weight/height. The effects that can be experienced vary based on tolerance level, the blood product being given (for ex: bone marrow tends has a longer recovery rate than just platelets), your overall health and experience with giving the blood product. The effects may be lessened if you are well hydrated and rested before the withdrawal.
That said, if you do have an iron deficiency (which, actually, isn't uncommon, but many people just don't know it), you may have effects that last longer or are worse. But they shouldn't last 5-6 days. Normally, the effects of the blood draw dissipate shortly after donation.
I think it would be a very good idea to call your doctor or the specific organization that you gave blood to (probably the Red Cross) to check. I've given blood before, but the side effects that I felt (dizziness, tiredness, a bit of nausea, etc) went away within a day or so. So I would definetly have a chat soon with your doctor or other appropriate medical personelle.