It can indeed take up to three months to replace the blood,
http://www.blood.co.uk/about-blood/how-the-body-replaces-blood/
but most people, if they have sufficient iron stores, make it up faster than that.
*Anecdote alert*
I once had a Hb of 7.5 g/dL post op, and 10 days later it was 10g/dL.
You should have had a haemoglobin check beforehand, and for you to donate it should have been at least 12.5g/dL. Your Hb after donation would have fallen to about 11 -11.5g/dL.
Normally a haemoglobin of this level would not be low enough to give the symptoms you describe.
Perhaps see your GP if these symptoms persist.