Put screens on your windows and doors. Lots of tips here: https://www.craftylittlegnome.com/flies-house-suddenly/
I have a couple of these magnetic screen doors: https:/amazon.com/d/Screen-Doors/Premium-Magnetic-Screen-Door-Retractable/B00CEFRCVO?sa-no-redirect=1
They work great, especially if you have pets that come and go. It will close behind them and keep bugs out.
bug zapper works, fly paper on rolls pull down to activate the fly paper, there are fly traps called rescue disposable fly trap, add water to the fill line, wonderful stuff. amazon might have them...
Hi Suze, we had this problem and realized our doors weren't sealed good enough. We added foam insulation (it has a sticky back) along all the edges and that helped a lot.