Site notices are not always required these days, only for larger developments which affect the community. However the planning department do write to all the immediate neighbours to inform them, so should have recieved a letter, thats if they did require planning.
Sometimes though people through these away as the Planning dept do not know who lives there, so just write to "The occupier", so many throw it away as junk mail.
I'd go to citizens advice first of all, as not a council matter, and they give free advice.