Hi - I wish you luck on your operation and hope it goes smoothly.
I can't claim to be an expert but if it helps I have read up on the subject a fair bit. From what I know, its best to avoid doing any kind of chelation for 3 months. Otherwise you could get mass amounts of residual mercury moving too quickly before it needs to settle. Read up on Andy Cutlers book - Amalgam Ilness. He has done some extensive research into this.
You could try taking regular doses of vitamin C as it helps to deal with headaches and various other ailments. Drink atleast 2 litres and more filtered water a day etc for hydration.