I put fly paper in our chicken shed and it got stuck to one poor chickens wings and in my hair, they are very cheap and very sticky, I suppose the odd one or two in strategic places may help!!
I lived near a hawthorn hedge boundary and that was really bad for attracting BIG flies, they of course will also be around in the surrounding fields on crops etc...those thunder flies (not sure of their name) are horrid when it comes to harvesting, all you pictures and clocks get full of them. You may have fruit flies so you could do with some local bats clearing them, not sure about having bats flying around the house, possibly worse than a few flies!!!!! There is also those electric fly traps that shops and restaurants have!!!!! If you shut the house up in the evening and leave an electric bug trap on while in bed, you should get rid of the ones already in the house, the main way to stop them comming in is close windows and doors etc