Lung problems and donating blood?

Patient: I have had breathing issues all my life and have 47% lung capacity. I have started to donate blood on a regular basis, and after the third donation, my breathing is worse than ever. I took up running and was able to run 10 minutes straight with a 1 minute walking break for half marathon distances. Last weekend I walked a half marathon and my breathing was awful and my lungs were burning. Could this change be a result of donating blood? Thank you in advance!

Doctor: