I used to donate twice a week for weeks on end back in the day. I was an endurance athlete at the time, so probably effected me a little less. Basically, it won't help. I would make sure you eat EXTRA protein and drink EXTRA fluids to compensate. I wouldn't work out right after you donate either (likely to pass out). Overall, I don't think it will hurt you too much, but don't do it any more often than needed.