Fair enough.
This third time, I ensured I did some exercise and drank lotsa fluids. Fate has it that I got a trainee nurse, brand new. She got the right vein but entered it wrongly - so I bled. Lost about 30 mls of blood. The more experienced nurse told me that it's going to bruise so I came home with a free tube of bruise ointment - which I intend to use on the enormous bruise on my leg.
I shall attempt to donate in 1.5 month's time again.