Try a bug off supplement, I had good luck with the smartpak brand one. I didn’t use it this summer, and I’ve gone through a LOT more fly spray. You’ll also want to up your fly control regiment. In other words, use more or a different kind of fly spray. Try rotating sprays also. Some work better for different kinds of bugs. I’d also recommend a fly sheet. You may want one with a belly guard.
I forgot to mention, there are quite a bit of bug off type supplements available, some you can make at home.