So the technical term for enlarged red cells is macrocytosis - and although pernicious anaemia is indeed one of the conditions where you expect to see macrocytic red cells, it is not the only reason - there are actually quite a few conditions where you might expect to see enlarged red cells.
And it is extremely unlikely for you to have pernicious anaemia whilst having a broadly normal Full Blood Count, as it appears you have been informed.
In fact, it is not uncommon to see enlarged red cells as a consequence of hypothyroidism ( under-active thyroid) itself.