Don't worry dibble, even RSPB checks nest boxes every year to find out which ones worked and that's nowhere near 100%.
Where you put nest boxes might not be where birds would choose to site them.
Birds like blue tits or great tits like tree holes so would be happy with boxes under overhanging branches. Robins prefer somewhere deep in the undergrowth. North, south, east or west is a matter of trial and error.
PS. Remember to clean your birdfeeders every couple of months to prevent diseases being spread to your feathered friends.