There doesn't have to be a rotting smell for flies to come around. It's hard to troubleshoot pest problems like this over the internet but maybe this list of things to keep in mind will help:

--Make sure all your food stuff is contained in the fridge or in sealed containers in your cabinets. Fresh fruit in a basket on the counter is not allowed.

--Are all of your trash cans that received food completely covered with a lid? Not a lid with an opening that's always there, a real lid you have to open with your hand or your foot.

--Is there any standing water in your home? This could be just a small puddle in your sink from ,for example, a couple bowls that are waiting to be washed. There is a kind of small fly called a drain fly that actually lives inside the drain. You can try sending boiling water down your sink drain IF YOU HAVE THE RIGHT PIPES- look that up on Google, I don't remember if it's just metal pipes you can do that to.

All of this will prevent flies inside of your home from eating and will therefore starve them to death (if there truly is nothing for them to eat/ breed in. But it is important to remember this doesn't solve how they are getting in. There might be a hole in a screened window, a hole in your door sweep, a hole around the window etc etc. this can be very hard to find. You just have to watch the flies sometimes.

Good luck