Hi LeoM,
it seems a bit odd seeing as he gave you a letter up to 27th Oct. With the weekly or monthly illness benefit forms a doctor is supposed to examine you and sign the form and you send it off yourself to the Illness Benefit section in Dept of Social Protection. Depending on a person's illness a doctor might not drag him in every week for an examination but I remember from my youth, an amputee neighbour calling into the doctor every week for a cert!
When you attend tomorrow, query your letter up to 27th Oct. Sometimes Doctors give unrealistic and inaccurate return to work letters also. Once, on hospital discharge after major surgery, I was given a return to work date which was 3 weeks too early. As you are genuinely ill you have nothing to fear from this new doctor. It should be just a matter of him signing an illness benefit form and you posting it away.
I take it that these doctors are your own business and nothing to do with your employer?